There are plastics, and then there are plastics - they're getting better all the time. Modern polymers are up to the task.
And yes, I'd prefer my safety to be frame-mounted and down-to-fire. I shoot Glocks, but I'll eventually have a 1911, cuz everybody needs one.
I've shot a friend's Beretta 92 and it's just a longish reach to snap that safety up, then bring my thumb back down to grip the gun to fire.