Tray said she thought the crossover writers were newer -- I assume she meant newcomers to the fandom, rather than new to writing or to LJ; or new in the eyes of LJ's HL community.
I'm having an interesting time comparing a group of HL stories to the "LJ house style." I've mentioned my interpretation of "present tense" in the OP; I've also noticed, in the first 20 or so stories that I read that the one element that didn't conform to the house style was the POV. I mentioned too (wherever that response is here) that characterization as a driving force in the story seemed a fundamental element of fanfic itself, other than gen stories posted on bulletin boards and the like.
I'm not wild about crossovers. I take the boom of crossovers, the kind of crossovers, currently overwhelming canon fic in Highlander as a sign of the fandom's deterioration.
Yes, there have always been crossovers in Highlander, though not as a majority of the writing, and not primarily abstracting Methos from the HL setting to play in another universe. There have been good crossover stories (you can't get any better than basingstokes's The Waters of Life and Death) and badly written ones. I think most of the crossovers being written now tend to be rather conservative in style. Most that I've read haven't excited me, though there are exceptions. Maybe it's just that since the majority of stories being written are crossovers, it's only natural that more of the weak stories fall in that category.
It has nothing to do with Duncan/Methos. Very few writers are writing D/M now. I'd love to see more and different slash pairings from canon. In fact, that would be a healthy sign. But Methos himself as the main export of the fandom is getting pretty tired.