The Danger of Underestimating...
The alternative 18..Rh8 gives white two good continuation:
[A]. The immediate 19. Nxc4 which is good enough for an endgame duel.
[B]. or the more promising
19. Nc6! Bxc6 (forced);
20. dxc6 Nb6 ( The alternative 20..Ne5; is simply meet by 21. f4 Ng4; 22. Nxc4!)
21. Nd5 Na8 (where else?; not 21..Nxd5? because the pawn recapture creates a connected passed pawn.)
22. Qd4! with the immediate threat of 23. Nxf6 isolating d6-pawn, (creating another weakness.)
or just the simple play 23. Qxc4.