Not so long ago I was involved in a discussion on stability.
I don’t think an efficient system exist - unless you build it ground up the Arch way.
If you choose any distribution you are presented with an initial layout defined by the philosophy driving the developers.
Stability has a different meaning dependinng on who you ask.
Plasma has never been stable for me - perhaps because I didn’t knew enough.
A couple of months ago I started experimenting - adding kwin to lxqt.
The experiment went well - and I thought - let me try the plasma desktop and I added the necessary components - and that went well too.
The key to a somewhat stable system is to have just enough components to achieve your workflow as adding more increases complexity and with increased complexity comes a degree of instability as there’s more components in play.
The amount of pressure you put on your desktop also adds a degree of instablility - especially with browsers - on a developer machine - if you are not very careful in coding your web apps - you can create a service worker which will crash your system without warning.
You mention several browsers with numerous tabs open - how many of them is running a worker service script in the background?
I see you changed the title of the topic - I am pleased I made you think - keep thinking.
In my experience - It is rarely the system itself that fails - but how it is used - perhaps strained - which makes it misbehave or crash.
Instead of hard reset You can use SysReq like described here [HowTo] reboot / turn off your frozen computer: REISUB/REISUO