It’s more likely that the PLAGF is pursuing a doctrine shift. The idea behind the 99A/B was that China didn’t need an expensive world best tank but a good enough affordable tank that was easy to mass produce and would perform well leveraging mass formation advantages. My read of the idea behind the Type 100 is that they feel both their armor and weapons tech have advanced to the point where they can employ that same kind of mass formation doctrine to win most tank vs tank engagements using a lighter platform that can then bank in some additional maneuver advantages. Maneuver advantages in turn probably allow for some shift in tactical formation choices which should be pro-adaptive to a new era of low altitude air threats. Ultimately though as a light tank with a smaller caliber gun there are going to be occasions where you still need a heavy tank to really hammer an opponent’s fortifications and reinforce your own, so having a bigger platform would also be desirable, and since China is no longer technology or resource constrained it would make sense to go bigger than the Type 99 series for such a tank. In short, I think the PLAGF is shifting to a two tier tank warfare doctrine rather than just a single mainstay platform with some light tanks for specialized ground domains. I expect the Type 100 to be the numbers fillers and this new heavy tank to be more of a complementary piece, and the Type 99 series to be phased out once the PLAGF is ready to introduce the new fighting doctrine en mass, which could take a few more years.
99 series were never 'affordable tanks'. It is the high end tank meant to stand against best tanks opponent could field, while type 96 was the affordable one. At the time the most likely opponent was Russia/Soviet Union, so Type 99 was meant to at least beat the T-72 and T-80s. Type 96 is the mass filler meant to replace the aging type 59 swarm. It has always been the two tier from start.
With that in mind I reject the notion Type 99B is the low tier tank. It is neither cheap nor worse than best tanks opponent has to offer. It can still beat advanced tanks from any opponents, from T-90S to Abrams. It is just that war has changed, and beating opponent's tank is a lesser priority.
Type 100 is a entirely different philosophy that prioritize defeating missile threats and possible drones. Naturally those threats require less weight on the tank than Type 99. I would not think it is light to be the filler tank analogous Type 99 and 96, it is a entirely different design philosophy, possibly not much cheaper than the 7 wheeler we are seeing. For the same reason I don't think the new 7 wheeler will fill the Type 99 niche of the past, they are different priorities.
If Type 100 can do almost as well as Type 99B (high end platform) in defeating enemy armor, then what point is the seven wheeler? To beat a hypothetical enemy tank design of the future? That feels a bit too luxurious for PLA tradition. I am not sure what they are going after that Type 100 cannot do, or making type 100 bigger. Because certainly Type 100 is not cheap, they would not be saving mass there to cheap out.
My only guess is the seven wheeler is meant to have some specialized difference that a bigger type 100 simply cannot do. This is why they carry those mass for specialized purpose, not just for sake of bigger gun and more armor.