I was just wondering what difficulty would be each type of league e.g bronze-hard platinum insane, stuff like that.
there isnt really a comparison as your playing a person when compared to a rigid construct that is designed to lose, ( if it wasnt it would win every time as it can perfectly micro and macro all the same time)
Agreed - AIs are very one-dimensional and not like playing people at all. They just send wave upon wave of ground units to your front door - the intensity of these waves ramps up as you move up in difficulty levels, but they don't seem to do much in terms of countering, massing certain units, or flanking.
There's definitely point in practising with them as that's basically what they're for. Just don't expect to master melee with them, that's all. You need to be more creative against human players as AIs don't train you in that department, only in the mechanical ones like hotkeys, micro and macro, etc.
I'd say very hard has a macro of top platinum/low diamond players. The first push they make needs perfect macro or ai abuse.