Do wide pullups actually work the lats better, or does it just feel like that due to the crappy mechanic situation you get put in?
No better, no worse. Just different.
Will narrow work the lats more by stretching the lats better in the bottom position and by providing better ROM?
Again, not better, different.
Does a thumbless grip take your biceps out of it,
No.
or is the way in which thumbless grip makes pullups harder simply due to the fact that you won't be able to hold on as good with that grip?
Thumb-less grip does not necessarily make the pull-up harder. In my experience, using a thumb-less grip or a full grip is a matter of preference and has no real bearing on how well a pull-up can be performed.
I like the thumb-less grip, it is more comfertable for me. Others may find a full grip more comfertable. Again, just a preference.
Are chinups actually better for back development than pullups because you can use more weight and thus better stimuls?
Who said more weight can be used with chin-ups? This is also something that will vary from person to person.
In terms of which one is harder, the pull up works your back muscles while the chin up works your bicep muscles.
Both types of pull-ups train both the back and biceps. Even then, the extent that biceps are used or not used depends a great amount on the skill level of the person doing the exercise.
The guy on the left, who has his thumbs around the bar is doing the pull up incorrectly as he's putting strain on his forearm. The guy on the right is doing the proper pull up as it will not strain the forearm which results in early failure.
If you are hanging by your hands, there is strain on the forearms. Their job is to help us hang on to things. Using a thumb-less or full grip does not change that, but like everything, there are differences with the way muscles are recruited when using different grips.
There is, however, an ever lasting debate about which one is best for back development.
I never quite understand when the "pull-up debate" comes around.
Why would anyone want to narrow down to only one type?
Would variety in the style of pull-up not be better than training only one type?
Do we do only bench press, cutting out dumbbells, inclines, push-ups and every other bench exercise?
Do we only squat, never doing a front squat, overhead squat, or single leg squat?
Different types of pull-ups are just like different types of squats or bench presses.
