A lot of BW seems completely obtuse on analysis but works much better in practice than altering things. There are lots of non-obvious interconnections and the system breaks easily. I have the sense that you haven’t played a lot of BW. My very strong recommendation is to play it as written, without modification. Play it a lot. Then, later, you can decide what you want to modify. But “it doesn’t seem realistic” or “it doesn’t seem right” or “it looks unbalanced” is likely to lead you into disaster. If you’re seeing wonder stats in BW I think it’s from lack of BW experience. I’ve found all stats to be very important in play. You’ll shine with high ones and suffer with low ones. There aren’t dump stats.
Here, at least, I think I can explain a little bit of the reasoning. I’m not an expert, but here are my best guesses.
Firstly, your descriptions are at odds with the BWG descriptions of stats. Agility isn’t fine motor skill, it’s hand-eye coordination. It’s the root for performing discrete tasks. Speed is for full-body motion, propelling yourself through space. Is this a weird distinction? Yes. And of course in the real world tasks don’t neatly break down between the two (and you need Power, too, for that matter). But everything from your fingertips to
Is the latter important for combat? Of course; it’s rolled a lot in combat situations. But not for swinging a sword, or swinging a hammer at the forge for that matter. That’s part of the balance: Agility is tested relatively rarely, and one of its primary functions is to be the root of stats, whereas Speed is used independently. Power isn’t a root for much because where it’s most applicable, combat, it already determines damage. Giving it more makes it too important. Forte similarly has few skills, but it’s what determines Health and MW and endurance. It’s not what you can do, it’s how long you can keep doing it.
Combatants require Agility for the roots of their skills, Speed for positioning, Power for damage, and Forte for their physical tolerances and Health. Change roots from Agility and there’s actually relatively little reason to have it over Speed.
Perception and Will, I just don’t see the discrepancy. They’re both roots for a ton of skills. Perception is rolled more often on its own; Will is more often going to be an Ob to someone else. Will is the root of those critical social skills. Perception is the root of critical Wises. And also not that counting skills doesn’t really give a good impression of total skill value. If Will were just the root of social and magical skills, well, that’s a huge and important chunk of stuff. You can make the other intellectual stuff Perception-rooted and not have problems.
I’ll reiterate: play first, tinker later if there are actual problems.
