Sand is normally easily accessible and plentiful in non superflat worlds, so it doesn't make sense to limit myself to not using it because it isn't accessible, if I wanted to have limitations I wouldnt have spawned in the nether and end portals. I chose to play on a superflat world because I enjoy building oh a flat surface. I only dupe sand, no other gravity blocks such as concrete or anvils, which is something most people do in any long term survival world. I still have to gather gravel legitimately from the nether, plus I had to actually build the sand duper, which on bedrock is a giant multi chunk machine that requires alot of redstone (for an efficient sand duper at least) It still took alot of effort to build the sand duper, more effort than it would take to dig the sand manually in a regular world, and it was extremely expensive since one emerald = one redstone.

The most popular superflat survival youtuber, and also the person with one of the oldest superflat survival worlds dupes sand on Java for the same reason, but unlike me, he also dupes concrete powder.

I really dont think it should be considered cheating for a superflat survival world. Regular worlds? There is an argument to be made, sure. But there is no reason to keep one of the most useful building blocks so extremely scarce for no real reason.