So...uhh...why don't we just not require magi to make these?
I mean, conceptually, it makes a lot of sense. The magus learns to interweave physical combat and spellcasting. If anything, casting defensively is what he does. Casting defensively seems like an excuse
As for 'violent motion,' I believe magus' training would prepare him or her to cast from horseback or in the midst of a violent storm in a way a normal wizard never could.
As for grappling, I can see the magus learning to mix mystical gestures into wrestling moves. Why wouldn't he or she know how to do this.
And, lastly, for taking damage, any frontline spellcaster should probably be able to cast through the pain, or they just aren't good at there job.
Mechanically, this gives them a bit of an edge/niche other casters don't have, and it's not like it's a gigantic class-making power trope. I mean, concentration checks have never been a huge part of games I've played, but they're a bit of a millstone on the magus' neck right now.