Unfortunately I have to disagree on this for the following...
1. Finder has been slow since Mavericks, and there's no indication Apple wanna fix that...
2. There's a nasty window auto-resizing bug on QuickLook since Mavericks which Apple still fail to solve...
3. The multiple text input cursor on Dashboard's overlay mode since Mountain Lion which Apple still refuse to fix...
4. Video playback stuttering for a minute or so on Mavericks and Yosemite. I see somewhat improvement on El Cap, but that doesn't fix the problem.
5. Safari has been a resource hog since Mavericks that when loading heavy-content webpages can cause VLC playback to drop frames. I can use Firefox as a temporary solution but that defeats the purpose.
As you can see, these are not El Cap-introduced bugs... These are leftover bugs from previous OS X that Apple either fail to fix or refused to acknowledge. So there's no way El Cap can be as close as SL.
Refuses to fix for the first beta sure. We have more betas to go. It'll get fixed with time. Or replaced.