Say vs a BTN open. I get that we can call way more but why does that mean we need to 3bet less? In practice at least I'm inclined to actually 3bet more because their ranges are weaker and will fold more (especially great when considering rake).
But I can't really articulate a theorerical explanation for why the opposite is true other than "as the RFI size increases calling sucks more so 3bet more" but it seems counter intuitive to widen a linear 3bet range vs a stronger open raise range.

I've never heard anyone say that you should 3bet more vs 2.5x.

You've gotta get a new coach.

vs 2bb


vs 2.5bb


Red is mandatory 3bet, orange is mostly 3bet. Are these no good then?
They're from respected coach

Vs a 2x the price to defend is just too good for these hands.

Also a 2.5x is more of an inducement to 3b because when V folds you in an extra .5bb

I think there's an argument that since you're defending more due to the decent price you're obligated to mix in more strong hands in order to balance your range. Also your opponent has better implied odds vs your 3bet. You can't really just 3bet against 2x and auto-stack off with top pair comfortably. You probably should 3bet less against a 2x range than a 2.5x range if the ranges are equally strong. I just don't all think that they are in practice. Mostly people employing 2x due so in order to have a better steal price and will widen their range as a result. So mostly, villain's weaker range allowing you to 3bet more is larger consideration than balancing for strength or implied odds.

Your coach also seems to be taking the "3bet less" to the extreme with his hand charts. Its extremely hard for me to believe AQo and ATs aren't even *mostly* 3bets against a 2x.

Calling means you play pots out of position while 3-betting slightly negates position advantage. The larger your 3-bet the less the enemy is obligated to defend.

Your original statement is only true given static RFI ranges. Meaning if someones RFI 45% then your 3b vs 2x is < than if they 3x open. If they start folding a lot more when they 2x open due to having a much wider range (50% RFI for example) then you can and should 3b more.

The actual [main] reasoning is because you win more when they fold to your 3b.... nothing complicated.