TL;DR: KDE Neon is an excellent distribution that's being hampered by its Ubuntu base when it comes to software. Manjaro KDE may not be as stable, but it doesn't suffer from the software issues that plague Ubuntu, namely an over-reliance on Snaps and having to reinstall your entire system every two years.
I've been an avid user of KDE Neon for well over 2 years. It's an excellent non-distribution that does arguably the best job at showcasing what the KDE Plasma desktop has to offer in this unfortunate sea of GTK/GNOME mess that is Linux. KDE Neon is by far the most stable version of Plasma you will ever find in Linux, period! You will never hear me speak bad about KDE Neon!
That being said, like you, I just switched back to Manjaro KDE for the exact same reasons as you did: the Ubuntu base has become over-reliant on Snap applications! Don't get me wrong, I love the idea of Snaps. I've been using Linux for over 23 years and I am tired of distributions creating their own packaging formats or their own variations of other packaging formats. It's gotten out of hand! We need a common package format that developers can write to, so we can get high quality applications, both proprietary and open source, on all Linux distributions quicker. The problems with Snaps are that they are terribly slow and they don't conform to your desktop's theme. If Ubuntu can fix these issues, Snaps will be great. Until then, they shouldn't force them on users; especially for system applications and libraries.
I have Manjaro KDE installed on my Surface Pro 4 (typing from it now). Switching back to Manjaro KDE did not come without some cost. The first being stability. I've spent the last two days working around bugs in Manjaro KDE that are simply not present in KDE Neon:
-I've used the Onboard virtual keyboard, with the auto-show while editing text and typing assistance (word suggestion) options on for the last two years in KDE Neon. I found out, after some trial and error, that having these options on crash the KDE Plasma System Settings application in Manjaro KDE. This is because these options rely on GNOME accessibility, and instead of ignoring this like KDE Neon does, Manjaro KDE freaks out and crashes the System Settings application. Turning the option off fixes it. There is a bug report in on this, but nobody seems to be working on it.
-I had a ton of stability issues with the Intel graphics driver and the HD 520 iGPU in my Surface Pro 4's Skylake processor. This is what originally caused me to leave Manjaro KDE two years ago for KDE Neon. I had to add a kernel parameter (i915.enable_fbc=0) to disable framebuffer compression, and I had to reinstall xf86-video packages to fix all of the issues.
I'm also dealing with a weird bug with Manjaro KDE's qtvirtualkeyboard that places the built in virtual keyboard at the top of the lock and login screens. It's supposed to be at the bottom. It also makes the virtual keyboard too big in Wayland sessions.
Oh, and I had to activate the testing branch just to get KDE Plasma 5.19.2. The stable branch is still on KDE Plasma 5.18.5!
So everyone in this thread needs to be careful when they throw shade at other distributions, particularly KDE Neon. Manjaro KDE has a ton of issues. However, Manjaro/Arch has excellent software repositories and documentation. Even though I spent more time then I wanted dealing with some unexpected bugs and stability issues, setting up Manjaro KDE was way faster than KDE Neon because most of the software I needed was in the official repositories or AUR, and most things are well documented. I also didn't have to deal with any Snaps!