1) MA man recruits them for 9 resources, so while they'd be more massable, even a completely unarmored guy with a wakizashi and longbow would be less massable than man's longbowmen.
2) Longbows are a lot more awesome when everyone isn't wearing plate and carrying tower shields. Even indies in la are hard to kill with longbows.
I can't see them working as your sole recruit without fire arrows. Until then, they just do not have enough damage output in the armor-heavy late period. Unless you're fighting manikin hordes or something else that doesn't have a shield. Plus you would still be owned by indy shortbows, who are more easily massed, cost less and actually have armor. There are maybe 8 LA nations whose expansion units are not nigh-invulnerable to longbows, and even fewer who could not adapt to deal with them just by changing what they recruit. I cannot see 12-15 resource longbows approaching overpoweredness in LA.
Squirrel - I think I agree with you on resource costs. Longbows are actually 3 resources in vanilla. Katana are still 7 though. And basic samurai armor 10
