APS cannot protect against KE penetrators effectively so base armor is still important. Unless you provide some sources specifically for advances in highly weight efficient armor it is hard to believe a mid 30 ton tank can achieve and likely exceed protection level of 55-60 ton tanks. ERAs has its own issues especially for constrained spaces like city warfare coupled with no evidence this new tank uses any leads me to believe ERAs would not make up the bulk of armor like on previous Chinese/Soviet/Russian designs with possible light ERA addons.Think you underestimate the material science breakthroughs in the last 10ish years.
Both ERA and base armor improvements might make this new 40ish tons next gen tank rival the 99A in protection.
And if you gonna say something about upgrading the 99A as well, then uh, it ain't no longer a 99A but like 99A+ or 99AG.
Not to mention, seems like base version of the next gen is gonna include APS, while that is not the case for the 99A.
As for upgrading ZTZ99As, me personally do not think it's a good idea. The design although comprehensively modernised from the original ZTZ99 but still has some carried over Soviet design influences which IMO isn't great for modern warfare. Plus if the heavy config of these new MBTs can match and exceed 99A's armor and firepower performance there is no reason to continue spending money upgrading them. It might in fact be more economical to start replacing everything with these new tanks for better economy of scale especially when there seems to be a entire system designed around the same hull.