if his 3b range is tight as you say (let's say AK, JJ+), then why would you ever flat OOP? seems to me the only way you ever make money is if the flop comes like A72 and he decides to cbet it with JJ even though he's in position so there's no need for him to do that. and even then you only get one street of value.

seems to me like flatting OOP against a tight range means that you always lose/split to AK, sometimes get one street of value out of JJ,QQ but usually either c/f flop or spew and get pwned by AA, KK.

as played c/f flop because the only thing we beat is JJ (if he has that in his range) and KK and why would either of those hands cbet on this board?