Technique and fitness are connected, but are not directly correlated.
you can be TECHNICALLY perfect (perfect form, great carved turns, etc.) but only be able to ski half a western run. I call this "eastern skier syndrome".
Similarly, lots of Western skiers that look effortless and amazing in powder can't ski rock-hard, no-snow-for-weeks eastern snow either.
Personally, I think the levels are a bit forced at the top end, and I tend to break it out.
you can be "level 9" at carved turns (smooth, effortless, linked turns in all sizes with dual carved tracks from initiation to finish and barely any "transition". Think railroad tracks.), a level 8 in moguls (can ski confidently but get thrown out of sync if they get real steep or icy), and a level 7 in powder. I'd say many very good eastern skiers would fit this profile pretty well. Powder, btw, doesn't really fit in the PSIA rating system well, it's just kind of tossed in around level 8.
The rating system is really more for level 1-6 skiers to help instructors separate groups into reasonable bands of skill so you don't have one kid wedging and another carving in the same class. Level 7 is where it starts getting fuzzier - there's a lot more room in 7 than there is in 6, because once you're starting to carve regularly it's just continuous improvement. There aren't any "key moves" (wedge, wedge cristie, parallel, carved turn, etc.) for 8 and 9, just confidence and experience.
I generally ask for a level 8/9 lesson if I'm getting one, and most ski areas keep this as one group unless you're getting a private lesson (or at least break it out after a run or two once they figure out a "slow group" and a "fast group"). 8 and 9 cover a LOT of range and conditions, and good instructors will figure out how to break you out to your skill level at each particular condition.
EDIT: Btw, I'm a former PSIA level 1 instructor (college meant no level 2 test), 3 years total instructing. Yeah, it ain't much, but the skiing levels get hammered in pretty early