Much better off. I tried to read the gor books once, sexism and dodgy BDSM aside it's badly written boring crap and I gave up after the first book.
As to john Carter, well without barsoom we might not get Flash Gordon later on, no Flash means nothing for Lucas to try and get the rights for, fail and go and make his own film. I suppose he might be inspired by Buck Rogers, but thats got sword and planet elements as well, and might be butterflyed.
Without ERB to start the pulp sci fi tradition SF, we might see Sf remain the sole playgound of serious authors like Wells. So more message and high brow, probably more respected, but a lot less fun.
No Tarzan will at least delay jungle fiction, and I think ERB did the first jungle girl story as well, so Shenna queen of the jungle, (the first comic with a female action lead, years before wonder woman) might get butterflied as well.
Also no Dejah Thoris, so the whole trope of scanty clad princesses never gets started.