kotl is really not that hard and a lot of people think he is. you dont get shard every single game and even when you do, knowing when and who you can recall for a certain situation is just general game sesne and hardly related to kotl himself. his laning is the most important part. i win about 80-90% of my lanes with this hero but i really dont think its incredibly difficult to learn who and where to blast and where you have kill potential if you understand laning mechanics well enough. mana - same thing. knowing who needs mana the most amd their approximate spell cooldowns isnt super related to kotl, just general game skill, and the kotl skill only comes in when it comes to nicher combos.

all in all kotl skill is largely dependent on general dota skill and the hero itself, mechanically and even strategically, is far from difficult, if you have said game sense.