no. let's say x=% of time villain folds, y=pot size and z=our bet size, then if x>(z/y), then we profit. i mean correct me if i'm wrong because i'm not reading this from anywhere or going off memory or anything it just stands to logic. the reason that fold equity is called just that is because our chance of winning (our equity) is of AT LEAST as much value as how often he folds to our bet because we win 100% of the times he folds. so the calculation isn't any different from any other equity calculation. you're still comparing how often you win to your risk:reward ration (where betting is the risk as opposed to calling under normal EV calculations).

in other words, big long explanation to tell you that you're overthinking it and FE is exactly the same as calling equity calculation wise.

as for this specific hand the donk is not folding a flush to anything including an all in. he's unlikely to fold a straight or a two pair, and we're really not all that confident he's even smart enough to fold KJ or AJ unless you just like over shove. we beat everything else so we don't want those hands to fold out. in any case his range of hands that he's folding is too thin to make turning our hand into a bluff profitable.