Well, 10 years ago or so, these splits were mainly for steroid users. I used to hear all the time that you can't recover fron a 20 some odd set workout on one bodypart without assistance. Like I said, I have tried it, I wasn't thrilled with the results but its time to try it again. And yes I am an insomniac and I like to drink and do drugs. that doesn't mean I can't hit the gym hard.
yes it can, and more importanly it effects your recuperation which makes your supposed hard workouts alot less effective.
split workout can be used by naturals. a natural can do 20 sets per workout without overtraining. but if your gonna do 20 sets per workout, dont go to failure on more than handful sets. (at most)
that being said, you can get great results from a simple upper/lower body split....so why dont you stick to that if you dont like to do split workouts?
also volume is something that has to be gradually increased so the body can be given time to adapt
also, doing a split workout doesnt mean you have to do 20 sets. you can do 10..you can do 11 or 4 sets. its up to you.
in bodybuilding the split you use (as long as its not totally fucked up) doesnt matter that much when you look at it in the long run...as long as your consistent and eat a caloric surplus with protein consumtion at 1 g /lbs bw and day.
do what you like, but make sure you have some kind of progression in your routine! (increase weights and/or sets, less rest between sets etc etc)