Your question feels like a trick question, but I'll answer earnestly.
what percentage of those game are garbage that you would feel like you're wasting your life playing them?
Cumulatively? Very low to where it's probably a single digit percentage.
Most of the games I've played in the past that happened to be garbage came directly from the PS1/PS2 generations when I was a kid, where I rented and borrowed games and didn't know any better. I played a few stinkers on gameboy advance and PSP as well. I've experienced the good and bad of those generations which is why I don't put them on as high of a pedestal as others here.
I've seen quite a few games here that some people claim to be garbage, that are average or above average at worst. Their tastes are so ridiculously high that they have lost sense of what a bad video game actually is. All they would need to do to get a refresher is to play something back then from companies like LJN, or Acclaim, 989 Studios, etc. to understand.
Even from saying all of this, I am understanding of the fact that the consoles I listed above have a ton of classic and amazing games, the same way I'm aware that in modern times we have had multiple gems that will be celebrated years from now. For some reason a lot of people lost sight of the simple and fun nature of what video games are as they chase the constant AAA high, and in doing so they have lost sight of the smaller guys with great ideas who put good content out quite regularly.
For some unexplained reason, just like Hollywood, people will give all of their attention and energy towards everything big budget and blockbuster, then ignore those smaller guys who make successful or well rated films at a place like A24...at least until their name becomes large enough to not be ignored anymore. It's interesting how things play out.