Thats unfortunate, I wouldn't really have called that ban worth, just should have been removed. I personally just use common sense when posting - if her tits are spilling out of her top which is 2 sizes two small and you can obviously see her defined nipples through it then I'd say something like that would be more fitting for /e/ since it's lewd. The picture that got removed clearly had the girls nipples visible and that's easily a no brainier - that picture was created to be lewd and is obviously not safe for work. Again personally I'd say that image is also not safe for work since you can clearly make out her nipples and it was most likely drawn by some guy who mostly does porn/smut.
If there aren't enough /c/ related images to keep a /c/ thread up then it shouldn't be forced alive and it should not include images that belong on /e/, /h/, or whatever mainly since there are reasons for those boards existing - what's the point in having them if no one bothers to post on the correct board? Doesn't mean these threads have to permanently have to end, they're always welcome on /c/ and will be even better after some time has gone by.
Sorry if I seem like a kill joy or something, it's just that not everyone likes lewd are or porn on /c/, I imagined that if people wanted to find others who did enjoy it, then they'd go to the board with like minded people.