Hmm, perhaps not pitch drift, a lot of vintage synths have very stable pitch - ironically sometimes better than modern synths. My System100m and MS10 are extremely stable, as is my MC-202 and TB-303s.
When I built my first x0xb0x it sounded markedly less alive and organic compared to a 303, I modified it to be less “plasticy and stiff” but none of it was related to pitch, but the filter, waveshape, VCA and power supply.
I really don’t like the sound of Arturia analogue stuff, it also has this kind of plasticy and stiff quality to it, I never bought any but every demo I heard was enough to tell. Obviously though this is personal taste, some people love that sound.
Another thing which possibly contributes to vintage/modern sound is things like how hard the filter is being driven, internal headroom and mixing, and even just good old fashioned noise floor.
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