I don't think that writers themselves or even newer fandoms progressed through each wave -- these are rather steps in the overall evolution or history of writing slash. I certainly never wrote stories that were first and second wave, though I read plenty of them. I don't think I ever "showed my work" either, which was one of the things that made my writing unpopular at first, and maybe still, with readers who prefer earlier styles of writing.
I think the earlier waves of slash in HL's history are a little bit different because we had a bit more plausibility built in. Yes, Duncan had quite a history with women and Methos was shown with three. But the characters also lived for hundreds to thousands of years, making the looser ideas about sexual identity easier to apply and sell.