Why LoL requires fast reaction and has difficult mechanics, but there no map to practice it?

When I started to play Heimer, I had to practice his missiles ult. And I had to wait cd after every cast. I don't think this is fair and logical. What if I'll want to practice Ryze combos, what I should do? Practice it on running bots? Or on minions that will be oneshotted?

What if you add map without cdr, resourse requiremens and endless gold? With dummy, and some preferences that can be changed: adding affects or items on dummy (like Banshee), resource endless or not, changing runes masteries without starting new game, etc.