>laggy, lackluster DE's and file browsers
That's a huge cultural problem with Linux. Their culture insists that they throw away old code and rewrite it or redesign it completely every two years or so. Hence, we have travesties like Gnome3, and the huge amount of unnecessary reimplementation work that went into KDE5.
The biggest problem is that it's hard to find people willing to fix bugs and make incremental enhancements in other people's code -- and yet that's exactly what Linux most desperately needs.
>screen tearing is quite often still a problem
Can confirm. Every single Linux system I've built, I've had to insert an NVidia card and use the proprietary NVidia drivers in order to get HD video play that doesn't have streaking, tearing, or stuttering.
Intel on-chip video, of course, is still totally fucked up on Linux. Last week I tried out the brand new LinuxMint 18 on an IvyBridge i5 system, and, of course, it had the usual problems with streaking, as always. So this problem is at least 8 years old and counting.
If it wasn't for the NVidia fix, I simply could not have considered a Linux desktop. That video streaking problem took me a lot of work and trial-and-error to find and fix, and few people have the the patience that I do to make Linux work despite the adversities. So it's absolutely no surprise to me that Linux desktop adoption is still under 2%. Most of that 2% must not give a shit about HD video, games, or much else. Most of them probably chose Linux so that they didn't have to pay the Microsoft tax just to use a browser, e-mail, and printer.
If you found a way to make Linux work with HD video and games -- then good for you -- you're one of the 0.01% geniuses, so go treat yourself to a starbucks today for being so smart.