Don't look at marks to calculate the cost of mounts, but to the Battleground rewards.
Before:
3 Marks win
1 Mark defeat
If we take a 50% chance to win (not always true, but will do for calculation purposes):
Average marks for a BG: 2
BGs needed to get 90 marks: 45
Now:
1862 honor normal wins, 3723(double) first random and first call to arms wins
621 honor defeats
With the same 50% chance
Average honor for a BG: 1241.5
BGs needed to get 50000 honor: 40.27
First random and first call to arms count double, so if they are 1 in 5 bgs you do, you end up with a number closer to 32 BGs for a mount.
I'd say 32 BGs for an epic mount is 71.6% of the work it took before, so I'll say it's a win.