I'm a professional and I occasionally look at the screen during a live performance... although I don't let the audience see me with my face jammed into the laptop. I like Mainstage b/c I can see the info on the screen on the sly from 5-10 feet away.
I agree, the looping in manstage sucks.
I'm trying some other looping plugs... guitar rig... sooper looper, etc.
Mainstage works pretty well for some things, but if you overload the computer it's gonna be nothing but trouble. I can't really say this enough... nothing will work well if the computer is choking.
I've noticed the presonus interfaces used with Mainsatage have a high rate of dissatisfaction in forums discussions. I hear ppl complaning about the presonus drivers.
I do know that different types of midi interfaces and different midi gear can have a wide range of midi latency, timing issues, performance issues and other problems. So it's possible that your hardware gear is contributing to the problem.
I've ditched the midi interface and am going with usb controllers, still hard to find usb foot controllers, check "eowave".
Another thing I've learned is that a mainstage rig still takes a lot of tweeking and tlc, you may free your self from the hardware and it's 30 min setup time but you will still have maintenance, diagnostic work, etc to be done. it can be overwhelming. If you look around (the videos above) there are a lot of people using it successfully but you need to work within it's limitations, having a crew spend a lot of time with it doesn't hurt either.
Another thing ppl overlook is the heat isuue, cpu's perform poorer as they get hotter. get a fan control program or an actual fan/heat sink thing if you're trying to do all that stuff on a laptop.