I'd argue it's the exact opposite. A second human and the associated space required are redundant when the on board systems themselves, possibly aided by AI, can deal with the workload and present the gathered information to the operator/pilot and give certain things priority over others.
In fact, the act of piloting itself may be somewhat becoming redundant, freeing the single human on board up to be concerned with coordination of unmanned assets, battlefield analysis and engagement of emerging threats.
Looking towards the US in particular, which has a true hard-on for their unmanned F-16 that flies mock combat by itself, I'm actually leaning towards the possibility these days. As in piloting the aircraft becoming secondary at best or even tertiary for the "Pilot".
I believe it's further supported by the simply fact that letting the computer fly the jet is basically happening already and has been for a couple decades already, in the form of autopilot. And while the application for UCAVs is what people look towards the most, I could easily imagine that this aircraft (X-62?) contributed a good bit to the US 6th Gen effort. Especially as Kendall was extremely fond of it. It also makes a lot of sense, as the truly "hard" decisions are what's left to the human operator. Having basically a large, capable aircraft with the associated sensor where the human component can completely focus on coordinating assets, assessing information and contributing to the greater puzzle of information gathering and engagements.
So I wouldn't be so premature in declaring the two seater option to be "for the better" aircraft of the generation. Ideally you'd have no seat at all, but technology isn't truly there as of now. But if you can achieve the same or even better results with a single person and the rest being done by the aircraft itself, I'm unsure if I'd declare increasing the amount of ballast in the aircraft as a positive. But it's so far too early to tell, with exactly zero 6th Generation fighters in service anywhere in the world.