As far as knockoffs go, I buy a fair amount of aliexpress “lego” but my rule is, only if I can’t buy the real thing from lego. Mostly that means MOCs, occasionally it’s meant something that’s totally unavailable. But if they’d let me buy it I would and tbh I’ve no guilt at all about that.
(I’ve actually bought genuine lego sets that I never would have, after seeing a knockoff on astrobricks and going, I want that, then googling and finding the original- so it’s not all one way travel)
I do feel a bit bad for some MOC designers- I’ve actually spoken to a couple of kit designers about this and both of them said “nah, we don’t make any money off it anyway and it’s flattering that our designs can be bought” but I know some people monetarise it which is totally fair, and I’d be amazed if lepin/etc have even once paid a single penny to a designer. But then, even if buying plans from a designer and then buying all the blocks specific for a build were realistic- and really, it’s usually not, it works out so expensive- I don’t want to hunt down bits, I want to buy a kit, open it and build it.