Ulhumbrus: After 18...c4 if White's advantage in space counts for no more than any other positional asset White's overall positional advantage seems only slight. In that case this suggests that the attack 19 h4? has an aim that is out of proportion to White's advantage and will fail. Better is Nd6 playing to occupy the d file.
However if the value of White'a advantage in space is greater than that and does justify playing for mate one alternative to 18 h4 is 18 g4 followed by g5 and then the sacrifice Nf6+ as in the game Petrosian vs Larsen, 1960
20 Rd4 seems inconsistent. 20 h5 continues the plan of the pawn attack g4 and g5. Perhaps Aronian wants to control the d file before starting the attack but in that case it may be better to play Rd4 before h4.
21 b3? advances a pawn against Black's queen side pawn majority and if it opens the c file in addition this will hinder more White's king side attack
24 f6 prepares to obstruct White's bishop by ...e5 as in the game Spassky vs Karpov, 1974
33 g4 suggests that Aronian has chosen a random target.
One can only guess the reasons for what appears to be Aronian's poorer playing form in this game. One example of a reason is that he was unlucky and his plans did not succeed.