Iirc manjaros problem is that its half arch in that it does staggered updates which doesnt mesh well with aur.
EndeavourOS handles the install so you dont have go through a complicated install just like manjaro does. But from there you basically have a barebones arch install with no staggered updates or anything. So all the kde packages should be up to date there too.
I did try manjaro forst and ditched it but i dont remember why.
I do use gnome though so take this with a grain of salt.
I can say I’ve never had a stability issue with arch though.
I have the same problem tab suspender addons really help with that.