I agree with both of you on that score.... lift and topography are
important. I will say that, in my experience, the ultralight planes have vastly expanded the range of sites and conditions that permit fun aerobatic flying. In the past, I had no choice but to fly a Weasel or Alula once the wind was under 10mph at my normal spots, meaning I had much less opportunity to practice "unlimited" (full 3 or 4 axis) aerobatics, but now I'm pretty much able to go crazy in about 6-7mph at Ellwood (the most typical of typical conditions there) and have been able to deal with on/off slermally stuff quite nicely at the Ruins, Greens Peak and Del Cerro.
But that said... if you want to fly just
like they do at Ménez-Hom... better go to Ménez-Hom!!
P.S. - And re: the latest videos of Rémi and Eric vs MH2005... Rémi told me that MH2005 was filmed in pretty epic conditions (for that site), which you can tell because there are few/no paragliders (too strong for them). I think these newer videos are more representative of the "average day" sort of flying they have on offer there: lighter lift, a lot more distractions from paragliders and spectators... harder to focus, less mental space to "stretch out", more stress. If that's true, it would also at least partially explain the preference for larger gliders (more efficiency, make the most of what's on offer). But that said, I suspect an ultralight plane would perform quite nicely in those conditions... hopefully someday I can find out personally