Upgrading Cube Aim 29 2013
Don't buy that XT groupset for that bike to solve those problems - it wont work.

XT is great, but it won't make your  bike more comfortable, and it wont make it better off-road. Worse, it wont work for that bike since it has V-brakes, and that groupset has disk brakes.  They are not compatible.

To make it better off-road you need (in this order) better forks, disk brakes,  better components (lighter and stronger) and lighter frame.

I agree with what others have said here: sell it, and upgrade the whole bike.  If you really can't do that, only go for SLX.