I think there is a big difference between maintenance and servicing.
The former being perfectly manageable at home with a multitool and for those confident enough bits for the brakes/chain (TBH I wouldnt be comfortable doing those without having been shown, its a bit subtle to learn of youtube).
Proper servicing on the other hand would require at minimum a work stand, wheel stand, vice, casette tools, hub tools, bb tool and plenty of space/time. Imo the outlay for tools could only be justified if you had at least 2 very active mtbers or a whole family riding regularly. For 1 person it doesn’t make sense, if you look after your bike it shouldn’t come over £100/year for parts and labour + a good shop will give you a warranty on work done and the knowledge that someone much more experienced than you has been over it.
Ofc if you fall on a shit shop that all goes out the window and i really don’t know many good bike shops, most random encounters ive had were laughably bad.
Im very fortunate in that my one of my best friends owns a bike shop and is a wizard mechanic 😀 He got me back into MTB’s about 4 years ago and built/serviced my first bike while i watched. By the time i upgraded to the Soul a year n a bit later i was confident doing general maintenance and all the basic parts of the build.
Now i just abuse his tools and bring him lunch or beer, still get him to do the indexing and spoke tensions as i doubt I’ll ever be that good 😛