Honestly, I just prefer to be the courteous type and ignore knocking out Gym mons who don't have a decent amount of defense time. There are also some Gyms on my College Campus that you're never going to have control of long enough to get coins no matter how strong your defenders or support/back up are. If I want coins I just have to go around to some very remote Gyms (like an out of the way lecture hall) long after classes end and drop Pokemon at them and hope one makes it to the next day, or just drop fodder that one go down in one shot on top of a bunch of Gyms throughout the day. Berries restore such a pitiful amount of CP that they don't really do any good at keeping a mon on a Gym if people are willing to just spam raid them and knock everything off in one session. There's no reason to care about your defender choice because the ability to sit on a Gym, keep throwing mons at the defenders, and heal them off for repeats favors the attacker to the point that there's no "if," only "when" for a single person sweeping up a full Gym. If I can use fodder to defend a Gym, why can't the attacker use 6 fodder to knock mine off? Their job is easier, and both cases end with the Gym battlers transferring the mon because it's not something they planned on healing it.
Honestly, I just really hate the way Gyms work right now since there's the limit on coins, it basically costs nothing of substance to knock a mon off, meanwhile you (in theory) expend valuable healing items when the Pokemon comes back even if it didn't earn you anything (whether for coin limit or it just went down too soon). Having the Pokemon bring back items on top of the coins would at least take a little of the sting off of them coming back too soon. I kind of wish they gave out Coins through something like Daily objectives instead of the Gym system, like 10 coins per day for doing your capture, spin, maybe for walking a certain distance in a day, battling something, using your raid pass, etc. Gyms could still offer MORE coins, but some way that isn't dependent on something as unreliably contested and poorly balanced for defenders as the Gym system.