Just on the above I don’t find my fs costs me that much extra in servicing. Bearings aren’t that expensive and if you do them yourself it’s minimal costs.
A shock aircan service is pretty easy and a service kit is cheap. Just a full shock service that’s a bit more involved.
With most fs bikes it’s not essential you do this that frequently anyway unless you do loads of miles on it.
Edit – to add I have both a hardtail and a 4 bar full suspension bike. I don’t really consider the fs to be materially different in terms of cost to maintain.
I use the ht for flowy but relatively smooth terrain and also for some steep tech stuff. The fs for everything else – you get hammered on the ht in anything rocky and fast and big drops etc.
Although I’ve recently swapped from an enduro bike (170f/160r travel) to a 130mm trail fs and so I suspect the ht will see less use as the trail bike is more of an allrounder and won’t feel so sluggish on easier trails.