Do you mean any given gaming PC sku in general or the Steam Deck in particular?
Deck *is* PC gaming in an enticing form-factor that does the best job yet of bridging various gaps. Having had one for a bit now as my first gaming PC, and with a nod at PC gaming's (and Steam's) seemingly steady increase in popularity, I think its in the realm of possibility for the Deck in particular to outsell the Quest 2 time-adjusted and assuming supply of components and manufacturing is not an issue. I'd say "outsell" is unlikely tho.
Based on anecdotal experience and perceived positive buzz, I definitely expect the Deck to blow past "a tenth" of
Quest 2 sales and probably Quest 3 (or the new Sony VR) as well. Thats assuming
what I'm reading about the anticipated specs proves true, i.e. a nice bump in specs but non-revolutionary in terms of the combo of features, low price-point and virally killer-app.