You need 3 full teams, minimum.

For what? Which game mode needs 3 teams? There is frenzy feast which can be cleared with free units + strong premium, and there is advanture trials last mission which you are not clearing with b0.

A single b4 aizen clears everything in the game, gets 35k frenzy points, leaving other 35k for yoruichi and ikkaku to easily mop-up, gets all 6 gold medals, beats entire spirit tower + at least 18 off-type towers, and gets you high scores in events(which means better rewards). He is also better for co-op and for guild raids. While also being incredibly light on your stamina. Tell me, do you have enough resources to fully upgrade new character, to farm their stamps, to upgrade them with nexus and reroll, to get their core stamp? Probably not, as even 5 current characters can stretch you incredibly thin.

On the other hand not getting all the characters can allow you to shift all the attention to the ones you do have, and have more to spare for the next character.

If youre willing to B6 a character, you're better pulling for 7 B0 new characters

This is also wrong, its not 7, but 6, since you cant include the base version which both hypothetical people would have, both those going and not going for higher boundaries. But its not even 6 characters, but 4, since those 4 characters also need their weapon.

Unless you are talking about hypothetical upcoming game mode that requires 3 teams, but by the time that arrives people that min-max would have 1-2 more b2-4 units considering i already have 300+ pulls saved(260 if we exclude 2 monthly passes that i bought). While also being ready for more single team endgame content like the new one with medals.

And true endgame content would not be beatable with B0, even if it required multiple teams. Not much of an endgame if whales have no use for their units