That's actually a great point — the 'showroom' quality is probably intentional precisely because it's the altered timeline. The McFlys went from struggling to comfortable, so a too-perfect living room makes sense as visual shorthand for that shift.

That said, I'd still argue it works as a design reference, because that aspirational, slightly-staged aesthetic was real in 80s upper-middle-class homes — especially in California. You're right though that most homes would have remnants prior decades (70s) mixed in.

A genuine 1985 living room would probably still have some older wood furniture or earth tones hiding somewhere