I have both an MH and an HPS and had the same understanding as you at first that the MH is better for veg. I have actually found the opposite with trial and error tactics.
There will always be specifics that people have different opinions on, but that's just me. I go with what works best for me and my crops.
My MH is used for nothing more then seeding and sprouting now. I run all of my plants to the HPS after about a week and a half under the MH.
To my surprise, the HPS sky rockets my plants so much faster than the MH for vegging. The only side affect that I notice, which isn't really a big deal, is the plants tend to bud a bit sooner then I would like. This usually starts about a week to week and a half before the flowering stage.
I still get fantastic results even if the flowering starts a bit earlier prior to the 12/12 cycle. I am running 18/6 atm. Hope this helps with your decision.