I'd just say it's useless because no two people can agree on what's important, so what's the point of giving a single score? And even something as seemingly simple as a compression algorithm has more than just two characteristics:
1) speed of compression
2) file size
3) speed of decompression
4) does it handle corrupt files well? (or at all?)
Even just looking at 1 & 2, everyone has different needs. Some people value 1 above all others, some people value 2, and most people are somewhere in between, and "somewhere" is a pretty big area. Yes, your examples are pretty far apart and most people would agree that "best" is somewhere in the middle, but the middle is bigger than you think. Hence, there can simply never be a "best". So why bother trying to score one?
> So why can't you create some kind of rating system to give
> you at least a vague quantifiable score of that concept?
Because it would just be too vague to be useful. I mean, yeah, it can sort out the great ones from the horrible ones, but that's easy anyway, so if you're just trying to compare a few really good ones, the difference isn't enough.
A car that goes 200 mph is great, but not if it gets 2 mpg. Likewise, 100 mpg and a top speed of 30 mph isn't useful either. If you're comparing a bunch of cars that get 32-35 mpg and go 130-140 mph, there's not a meaningful way to pick the "best" in that group that everyone will agree on, unless one has the highest speed and the best mileage, but then, again, that's an obvious winner and you don't need an algorithm's help to pick it out of the pack.