Cass: I think donking some of our stronger flush draws is enough to balance in that spot, considering how hard it is for us to have a strong value hand when we check preflop (can't have AA/KK/AK/AT+). We don't have many value hands in our leading range, so we don't need many bluffs. We could consider adding some of our stronger Ax hands (A5-A9 perhaps) into our leading range for value since other players are unlikely to limp stronger aces very often, but then we'd have to add a few more bluffs, like maybe 54 with one diamond or QJ with one diamond.

I think you need to be donking in limped pots like that, yes. It's going to get checked around a lot, and you're going to lose value. The occasions on which I would c/r for value instead of donking are rare – very few players are inclined to limp in and then show aggression on the flop, so you're usually going to have players calling bets more often than making them, which increases the EV of donking. But in certain circumstances in heads-up limped pots c/r might become a little better versus an aggressive opponent. Check-calling there isn't something I would ever do with a hand that strong – mostly just doing it with semi-strong value hands and occasionally with weaker draws, depending on betsizing. We're always going to be check-folding a lot on most boards given how wide and weak our BB range is there, so it's not necessary to worry about being exploited too much – players who limp in a lot aren't capable of exploiting us anyway, usually.

Joel: I would strongly recommend drastically reducing your donk leading frequency. Obviously donking is something you can do some of the time, but if you're donkbetting every time you hit any piece of the board, then a) as soon as you check, your opponent knows you have nothing and can bet 100% of their range and pick up the pot 100% of the time, and b) the weaker parts of your betting range are going to be in serious trouble once you lead out with them. This is unlikely to be compensated by the EV you gain with the stronger parts of your range, since your opponents are likely to figure out that you're never donk-leading as a bluff, which makes it much harder for you to get any value from the stronger parts of your range on later streets.

If you had to choose always checking or always donking in the big blind, it would probably be better to always check. But you don't have to do that, so try to think about mixing up both your checking range and your donking range so that you're not playing quite such an exploitable style. Honestly, if there's any part of your game at all that hasn't changed in about 5 years, I imagine that part is going to be costing you money.