It isn't. OH CFOP movecount should be lower than normal CFOP. Mehta, on the other hand, shouldn't have a big difference in movecount between 2H and OH because it's heavily alg based. Ultimately, their OH movecounts should be quite similar.Mehta has a 45-50 movecount, which is way better than the movecount of CFOP
As a ZZ solver who solves rotationless, I disagree. Rotations don't take much time, whether it's OH or 2H. And good CFOP solves should only have around 2 on average anyway.and Mehta is rotationless, which will help avoid table abuse and save a ton of time
Lastly, erognomics. I argue CFOP has better OH ergonomics than Mehta.
Also, there's the practical disadvantage. You'll have to actively practice 2 completely different methods.