for a total of 5.5-8 stacks per turn (+1 when aventurine gets to fua, +0.5 if he ults as well, +1 if numby is in ult and gets a 2nd action)
The main difference this will make for the premium fua team is that against more aggressive enemies and aoe enemies where Aventurine can launch more fuas you're more likely to hit the cap of 6 extra stacks per turn.
For lower investment teams (MHunt/Moze) it won't change much. For hypercarry teams with no other fua sources (non-e4 bronya+feixiao hypercarry) it's a slight nerf compared to V3.
Topaz will become more important as she provides an extra stack every turn, and more if numby gets to move again.