Sounds like YOU did everything right, but I completely disagree with your mechanic. 2 quarts between changes is NOT normal. Some consumption is, sure, but that's excessive. If valves are getting "sticky" that indicates something's going on. My guess is due to your oil consumption and "sticky" valves, you had leaky valve seals. Since you spent a decent amount of money on yours, and if you liked it and want to drive it til the wheels fall off, my suggestion would be to just do a head job (by somebody who knows WTF they're doing). I am HIGHLY doubtful it needs a new engine. A different high mile motor has questionable history, and your block's likely totally fine. Your head's probably totally fine too (would need to be verified by a good machinist). That's why on both my last engine jobs, I decided to stick with my own engines and redo the heads. On my S60, the head was in beautiful shape. Just needed new valves (that were completely mangled when I bought it). Shops these days must be overwhelmed it seems, as 9 times out of 10, they suggest the lazy way out (motor swap) instead of doing actual mechanic work and FIXING the problem. The previous owner of my S60 took it to 3 different shops, and I called around 10 more. ALL of them said it needed a new engine. It did not. In your case, it seems awfully wasteful to junk a whole perfectly good engine over a pack of valve seals and some valves, assuming that's the root issue and main problem that led to the burnt valve. Yes, it's a lot of work, but it may be worth it if you like the car.
These dudes: https://usparts.volvocars.com/p/Volv.../31430939.html
Here's the before and after of my S60 head:
Attachment 475381
Attachment 475382
And I'm FAR from a mechanic. I'm just some yahoo screwing around in my garage. If a trained professional mechanic can't confidently do a head job like I did, then theyz a bitch. :D
Out of curiosity, did your indie actually run the car through VIDA (the factory Volvo diagnostics software) or do any deeper diagnostics than an educated guess?