I think it depends on where new folks look first. LJ is fairly diverse, with lots of different pairings and crossovers and all. But Seventh Dimension is still the first hit that comes up on Google for 'Highlander fanfiction' and IIRC, it's heavy on the DM/M.
Given how much sniping and wankery I've seen reported from other fandoms (HP and DW, for example) I'm just glad that even if DM/M continues to be the most widespread pairing it doesn't seem to be igniting any nasty wars about who belongs with whom and how much you suck if you disagree. Granted, I came into the fandom late and probably missed any such things if they did happen, but it's nice to not see it now.