I like libinput, appreciate pulseaudio, and I don't have any real hatred for systemd.
Then again I use the CLI to tweak all of the above, I wouldn't be surprised if the recent libinput switch for almost everything has resulted in significant GUI carnage.
But that's also why I completely agree with you in regards to DEs.
My main problems are that libinput doesn't like to let mice be completely 1:1, and in the Wayland era they're going to be pushing responsibility for config out to DEs, where effort will have to be duplicated a lot (what config there is, anyway - they've definitely got Gnome's philosophy on that). The acceleration it decided to apply by default is of atrocious quality. I got a top-quality mouse for a reason, and I don't appreciate anything that ruins that. As I said, there'll be another rant incoming on that in a bit.
Pulseaudio uses enough idle CPU time to peg my CPU at max frequency (intel_pstate governor in powersave mode on a G3258). Systemd works mostly alright for now, but has philosophical issues.
Designers aren't trying to screw up. They are laboring under some impossible restrictions, though.
1) A new UI needs to be flashy to draw attention to itself, so that you know you're using it and it gets mindshare. Also, it needs to be unobtrusive and out-of-the-way for day-to-day use.
2) You can't use an older UI because it's a stale, bad, old design. But the new UI needs to be just like the old one so that it's easy to use.
3) You need the interface to be optimized for the device. The device is a phone. The device is a tablet. The device is a desktop. The device is a workstation. The device is a television. The device is also a kiosk.
Those aren't supposed to be tough restrictions. You can use an older UI, and it doesn't have to be flashy. It doesn't take much extra to make it feel new-ish, if that's the goal, and the old thing is proven to work well. Then again, razor-thin phones with no durability and no battery life are the ones that sell, so what do I know?
Also, like JBI and you said, using one UI for both mobile and desktop was a garbage idea right from the start.
Is that the equipment you are testing these DE with. Because that is some really old and slow equipment. Linux development has moved past this lowest rung hardware for the most part and you need relatively modern equipment for it to feel snappy. In general, I agree with your sentiment. While I appreciate the choice, I think linux for the desktop environment would be better served by focusing talents on making a couple of options great.
Personally, I roll with LinuxMint & Cinnamon on my primary laptop, Win10 on my gaming machine, CentOS/RHEL w/o GUI for servers. =)
I test on a wide variety of stuff, from junkyard machines like I just described (or worse) up to my own G3258 @ 4.3 + GTX 960 + SSD rig. I'm fine with games having high system requirements, because more often than not you're actually getting something for it. When DEs have high system requirements, you get next to nothing that actually matters. The core functionality of a DE is, in theory, near zero load compared to a web browser or something. Hence I get really annoyed when I see a setup that can browse the web alright but struggles to open a menu on the desktop.
I know from lots of experience that LXDE will run like greased lightning on computers most people would say are too old to warrant a second thought. LXDE doesn't have much eye candy, but it does what a DE needs to do as well as the best. Being able to run fast on a toaster is supposed to be a big advantage of Linux (and it is one that I take advantage of regularly), but there's a very big crowd now that would throw that all away for a bit of bling. Not only that, but they've apparently convinced some people that medium system requirements are just the way things are.
You know End User's world where the solution for everything is "buy better hardware"? I have a lot of friends who live in pretty much the exact opposite of that, and in that world, software speed is a really big deal.