I need a chess analyst to explain the engine's evaluation

So I played a game today:

1. d4 Nf6 2. c4 d6 3. Nc3 c6 4. e4 g6 5. Nf3 Bg7 6. Bd3 O-O 7. O-O Bg4 8. h3 Bxf3 9. Qxf3 Nbd7 10. Be3 e5 11. d5 cxd5 12. cxd5 a6 13. a4 Rc8 14. Rfc1 Qa5 15. Rab1 Qb4 16. Bg5 h6 17. Bd2 Nc5 18. Bc2 Qd4 19. Rd1 Qc4 20. b4 Ncxe4 21. Bxe4 Qd4 22. Be1 Qc4 23. Bd3 Qc7 24. Rdc1 e4 25. Nxe4 Qe7 26. Nxf6+ Bxf6 27. Bd2 Rxc1+ 28. Rxc1 Re8 29. Re1 Qd7 30. Rxe8+ Qxe8 31. Be3 Qxa4 32. Qxf6 Qd1+

On move 16, the engine says that I made an error by not playing 16. bd2. However, I ended up playing it on move 17. The only difference between these positions is that Black's pawn is on h6, so how is it more than a point worse?

You helped black to develop and gave him free tempo. Apparently 16. Bg5 didn't create a weakness.

I understand he gained a tempo, but the only thing he gained was h6. im not understanding why white drops an entire point in the evaluation. The bishop ends up on d2 anyway. That's a huge shift from such an innocuous move and I dont see how it plays out in practice.