I think it is fairly marginal (i.e. you can mix it up without much loss of EV) to cap pre vs donk the flop vs. c/r the flop. I don't assume nobody can hand read - if 1/2 villians can than not capping is prolly better to info hide and play more aggy OTF, OTT, etc. The problem with a 21 sb pot (assuming IP bets and you c/r OOP) is that even facing the field with 2 bets cold is only 10.5:1 odds and they will likely call with almost any piece (and be correct). If you wait to the turn to c/r you could still not cut down their odds that much depending on action OTF.

Since you didn't cap - it looks more like you could have a 9 than if you capped - since they would put you (even droolers) on a QQ/KK/AA hand - maybe AKs - none of which can rep the straight on this board.

C'mon guys, this is a super standard cap PF. Our opponents have to be capable of thinking to even think of possibly entertaining not capping here 3-way, but with 4 players who are likely droolers capping is clearly the best decision. Your hand is huge equity hog, take it now, bloat the pot, and make them want to call you down because of how big it is.

The rest of the hand is good. If I cap PF I obv lead the flop but just bet it down.

I wasn't advocating not capping. I was only addressing your concern of the flop checking through (in case a good reason for not capping was found, like having 2 or 3 competent players seeing the flop)