Do you need the upmass of the superheavy to launch the satellites used in the Starlink constellation? The answer is no. Elon only made the superheavy because he supposedly wants to go to Mars and he wanted to get the NASA funds for manned lunar exploration. If you look at the NASA specifications for the lunar missions they want the capability to send a huge amount of mass into the Moon with a single flight.
But other people have shown that unlike the NASA mission profile it is perfectly possible to achieve such missions with something like F9 Heavy and multiple launches.
A fully reusable superheavy will change the way that satellites are made. You have to understand that satellite design are heavily heavily constrained by launch prices, mass and volume. A launch platform like Starship will change that. For the most famous example, consider the JWST. Why? Because it had to be folded up to fit into a tiny fairing of an Ariane 5 and had to shave weight every way possible. The chief designer of the JWST has once said that if he had the option of launching the JWST on a platform like Starship or SLS, the JWST could have cost a fraction of the final price due to not needing to fold the telescope and having a lot more mass to to work around and they didn't have to risk the unfolding process destroying the telescope/mission. Considering that JWST cost around 10 billion, that's a fair amount of money and development time that could have been saved, that's a decent chunk of SLS and Starship's cost right there.
All satellites have this issue. Even an off the shelf cubesats have to shave off weight whenever possible. So they instead of cheap and heavy steel, they have to go for lightweight expensive aerograde materials, they have to go with the bare minimal size for their solar panels, they have to go with the bare minimal of reaction mass, they have to go with the bare minimal of radiation shielding, they have to fold their solar panels and antenna to fit within the fairing. Billion dollar deep space science missions have limit their instruments/sensors.
Do note that the folding of the solar panels and antennas are still an issue. The recent Lucy missile had issues when it's solar panels failed to unfurl and there have been plenty of very expensive spacecraft that have been lost or couldn't perform to their fullest potential due to their solar panels or antenna not deploying properly.
Now imagine if the costs fell so much that you didn't have to shave every gram of weight off a satellite, they would of course be easy to make. You can pack a satellite with an immense amount of extra fuel, especially for the evasive manoeuvres that spy satellites like to play with each other, or for more important satellites to last an extra long in orbit. You can pack a satellite with tons and tons of just raw mass for radiation shielding so that you can operate in enviorments like the van allen belts or if you want to fit your GPS satellite with the best electronics without having to worry about radiation wrecking it.
You can use off the shelf solar panels instead of insanely expensive multi-junction thin flim solar cells. You can just launch a particularly expensive mission with it's solar panels and antenna already deployed and not have to worry about them unfolding in space, extremely expensive missions like the Mars sample mission that you don't want even the slighest chance to fail will greatly benefit from this. You can launch massive payloads like entire space stations without having to assemble them in orbit. In this respect for volume, you need a superheavy like the SLS/Starship/CZ-9 , only they have the fairing volume for this to make sense, even if you think that a Faclon heavy or triple core LM-10 is cheaper and can also get the job done. Suddenly you can make cheaper satellites, at the expense of them being heavier and larger, but mass and volume and cost won't matter so much with a launch platform like Starship.
More power is another area that satellites can never get enough of, considering that many mission profiles directly scales with power, like ion drives, sensors, instruments and anything to do with the EM spectrum. The ISS has the largest and heaviest solar arrays in space and it's enough for 240 kilowatts... Not a lot by comparsion to earth based systems. Especially as space warfare heats up and suddenly you're wanting ever more and more power for jamming, propulsion and maybe even energy weapons like lasers or mircowaves. And of course, that's a lot of mass in solar panels, and with all that power comes extra heat, which means extra radiators. The mass requirements go up fast in that regard. And there's the wildcard of space based solar power to consider.
There's lots of other mission profiles that might open up in the future. For example, if orbits are filled with hundreds of thouands of satellites which will likely be reality in another decade, then suddenly anti space trash systems like space tugs and refueling spacecraft are suddenly extremely important. Do you know how much fuel it takes to change your inclinations in orbit, or to deorbit something? Such space tugs or refueling spacecraft will have to be 90% fuel by mass if they want to reach more then a handful of satellites. Again, a fully resauble low cost rocket might be useful if you want to launch a 100 ton spacecraft's 90% raw mass(fuel) to orbit every week to prevent valuable orbits from becoming trashed by the exponential increase in space trash.
Fuel depots is another thing that a fully reusable superheavy enables. Raw bulk mass in large amounts, like you yourself said that it fits a superheavy profile. And you might ask, what's the use of fuel depots? Well there might be uses for them in lunar/Mars missions and deep space missions. But I think their main use will be in the forementioned space tugs and refueling spacecraft, espically if the trends continue and we end up with hundreds of thousands of satellites sharing LEO and suddenly redunct satellites are a regular and expensive problem.
Oh and deep space missions are a massive boost with a superheavy. Sure you could launch a Jupiter mission on a medium/heavy lift rocket, but it will take 20 years and a few gravity assists to get there. Or launch it on a superheavy and have the spacecraft arrive in 5 years. Take your pick.
The only reasons to use a superheavy are if you either have an indivisible payload you need to put up into space, or you have to put so much upmass in orbit that it justifies the huge expense of building the superheavy and its factory. The current requirements worldwide for indivisible payloads are supposedly one flight every two years, with a max of one flight every year in the future.
And do you really think that people wouldn't adjust their satellites to take full use of a superheavy? Have you maybe considered that maybe why space agencies aren't sending up massive satellites and telescopes is because the only superheavies in service right now is the FH and SLS, with the SLS barely functionable. And the FH barely counts as superheavy and it's fairing size is the same as the F9, which greatly limits the missions that it can launch. This is putting the cart before the horse. Of course nobody would design their payloads to only fit a superheavy's mission profile when there's only really the FH flying reguarly. As I have said before, the volume matters of the fairing matters alot in this case. Even then, the FH only took it's first flight in 2018, there's probably lots of satellites designed for it that haven't finished building yet, considering the lead time for space projects is around a decade.
I don't think you understand that satellites have to be designed around the rockets that they are launching on and not the other way around. Do you have any idea how much science missions to deep space are neutered because they didn't have the mass budget to fit an extra science instruments, didn't have enough power due to being unable to fit as many solar panels as they wanted- to the point where some satellites can't power all their instruments all at once and have to cycle though them , couldn't add redundancies like an extra set of batteries or extra fuel for course correction or took an extra decade to arrive at their destination because they had to launch on a low energy orbit on a medium lift rocket.
