BTN was extremely loose-aggressive preflop but far less so postflop.

We're just so deep and I want to isolate. It's loose, but again: we're just sooooooo deep and villain is opening wide and seeing a lot of flops.

I just didn't feel like there was much point in betting: check/calling with the overpair and the FD.

Pretty cool turn, but I check due to what I thought was a high likelihood of villain continuing to bet: the board is very draw heavy and if they had a strong hand on the flop I don't know that slowing down makes sense super often.

Filling up on the river, I decide to bet half-pot for two reasons: I don't want it to check through but I also don't think villain's range is very strong here.

But when villain raises so much, I'm pretty confused about what to do. If I 3bet, I'm strengthening their range to remove virtually all bluffs and increase the likelihood of 66.

Certainly they can call another bet with worse, but how do we size it here to get something as weak as 63 to call? Maybe even A6? Keep in mind that I'd pegged this player as far less spewy postflop than they were preflop.