Its all speculation unless you get access to the lathe...even then, lathes wear out from use, lack of oiling etc that have never seen a grinder. For that matter, just because there is a TPG, maybe it was used 2x in 20 years? who knows.
End of day, wear is wear. The key is to assess how much and whether you can live with it (A little doesn't make the lathe useless, a lot can be problematic, like when the carriage stops riding on the V lol) or fix it. (reconditioning, BIG job, make sure the lathe is worthy).
btw, Grinders don't put out much abrasive except when dressing (then its a free for all). I try and give extra protection when dressing, e.g. cut out carbard box to contain a lot of it. If you've much grinding wheel wear is very slow so there is not much abrasive come of during grinding. If you example the sludge after the coolant dries(yes, I lead a charmed life
) its chips (fine) not abrasive. I have a T&CG set up for cylindrical grinding so don't often use a lathe, and while I'd prefer to minimize it, I'm am not adverse to it. I can only internal grind at the moment on the lathe for example. Everything gets sealed off with paper twoels held down with pot magnets (rags can be dangerous around machinery).
as for the spindle, in larger sizes (threaded is the norm with smaller sizes), a threaded nose is pain in the rear compared to cam locks However it limits very few things you can so is infinitely better than no lathe
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