I can tell you that you're not alone in this assertion.
I think 9 is better but my conversations with others in the last week or so led me to believe that way more people than I thought adored 10 more than 9. Likely because 9 captured the spirit of 2, and 10 was more along the lines of 3/4 with some MMX4/Bass trappings (but that's mostly relegated to being able to pick from different characters at the outset).
Mmhmm, at least on GAF the verdict is pretty clear, but it's not completely a shutout in favor of 9, even if it feels like that's the case. That sort of balance reflects the general sentiment outside of GAF too (on fansites, or even the odd thread from Giantbomb or whatever) that I browsed through recently. It's a minority opinion but I'd expect at least a couple people in any decent-sized discussion to throw a wild 10 vote.
Your other idea on the appeal of 10 does hold true for me, as I am huge fan of 3 and 4. Incidentally Mega Man 4 has its own small and weird defense force too, but it's very small. =P
I'm with ya, brotha. And this is coming from someone who likes 2 the most.
=3
I do like Mega Man 2 a lot, just not as much as 4 and 3.
It's hard to deny how iconic the Robot Masters are. I remember being in elementary school and trying to make sprite comics based off of Mega Man, and a handful of classmates were like: "Oh! You mean Bubble Man and Heat Man and Quick Man and..." This was during the bridging between N64-GCN and PSX-PS2. I was totally surprised. Most of my classmates only knew about the 2nd one somehow, besides my one other friend who played Mega Man a lot too.
The game's cursed. It's voodoo.