The typical buyer thinks in this exact same way (talking SFR now). Anyone that's worked with buyers knows that's the case when they walk thru houses and say something like..."I like this kitchen better (+) but I like the bathroom in that second house better (-). They don't say "I think this slightly updated kitchen is worth $2,500 more than the last house" or "this house has an extra 75 s.f. that has to be worth about $40/s.f.".
I agree, having sold RE, that is how typical buyers think, though they are aware of costs and assuming well informed, they have a rough idea of what upgrades cost to put in, or what repairs cost to fix.
While it is true that buyers themselves don't make adjustments, an appraisal is more than a direct reporting of what buyers do, it is an analysis of what they do ( and how markets react to what they do). Because an appraisal is an analysis , we make adjustments for patterns of buyer and seller behavior. The buyer likes a kitchen more (because it is upgraded), market data shows most buyers paying 5k average for updated kitchens in houses of subject size/ in the area. Of course a degree of price variance has no clear explanation and that is part of the market as well.
Very small adjustments and adjustments for minor differences are too hard to extract and thus are better off addressed as qualitative factors.
I personally think an appraisal using plus and minus with narrative could be credible, but would not be accepted, at least not now, by lenders and the secondary market.
Since adjustments can be "off", referring back to the un adjusted sales prices is useful.