because of SB's bad squeeze sizing and what our position's going to be postflop, we have to 4b preflop. it's more standard for him to squeeze like 1.80, so this sizing, when we just flat, allows CO to get a preposterous price IP in a 3-way pot to call with PP's, SC's and other various implied odds hands. when he calls, we're going to have terrible relative position and significantly reduce our profitability in this spot.

i think raising the flop is silly because, as you say, the chances of someone having a draw are slim-to-none (the only chance is if CO has 76s, and he may decide to semi-bluff raise that anyway). there are like no scare cards and there's only a PSB left behind so we're getting AA/AK's stack regardless. flatting allows us to the chance to possibly get KQ's stack (if that's in his range) and for him to make more mistakes with JJ-QQ.

the turn is kind of an awkward spot because we only have one PSB left behind, and really we're trying to maximize our value against marginal hands like QQ-JJ, KQ, while assuring we're still getting AA/AK's stack. surely we're getting snap folds from his marginal range if we simply shove the turn, yet checking leaves room for all types of scare cards to hit that will 3-flush or 4-straight the board (scare cards for villain, of course, we're winning the hand just about no matter what).

i'm somewhat inclined to ghey bet this turn like 2-2.40 to make him feel priced in with most his range. this leaves behind what seems like a perfect amount for villain to shove over if he feels like spazzing out with AK/AA/KQ, or if he falsely thinks he now has FE with AdQd. I also doubt he's c/c'ing this turn with AA/AK only to c/f to a <1/2 PSB river shove when a third diamond hits. MAYBE he finds a fold if the board 4-straights, but overall i think we stack more frequently by leaving us less money behind for the river.