If you can't handle it, then it's obviously is a higher level of training. The truth just hurts. You think MMA fighters can't go to your gym and memorize kata?
It's a different type of training, not necessarily "a higher level".
And there's also a difference between not being able to handle it and not having any interest in it.
I wouldn't expect an MMA fighter to have much interest in coming to do patterns (some might though), so they'll likely have trouble remembering them due to lack of interest.
I don't want to train MMA (that's the style btw, not the literal meaning of different arts), just like I don't want to work in an office again, and I don't want to go to the dentist.
Also, the level of intensity you put into your training is down to you, not the style. You can slack off in an MMA gym just as you can push yourself anywhere else. The coaches in an MMA gym won't force you to try harder, they'll probably encourage you but if that doesn't work they'll just keep taking your money until you quit.