Not only did you entirely miss my point, you clearly don't understand and don't want to understand.
You're literally saying "people have abilities they can use strategically in tandem with their champion to make plays and get kills/objectives or win trades" and using it as the claim that the game is somehow broken.
The fact is the game is balanced around summoner spells, rather than them being an afterthought like you seem to think they are. Flash is the reason why we can have hypermobile champs without making immobile ones useless, because it gives them a one time reposition that they can use strategically to win a fight.
Darius is balanced with the possibility of him exhausting you in mind. Zed is balanced with the possibility of him taking ignite. Mundo is balanced with the knowledge that ignite exists.
You don't seem to get that summoner spells are a tool that everyone has equal access to (pre-30 play is basically a joke, it doesn't matter). You also don't seem to get their optimal use... Darius shouldn't use flash and exhaust to get onto you. He should hook you, slow with W, exhaust when that ends, and follow your flash attempt with his. Alternatively, he could exhaust to set up his hook, but he doesn't get as long a slow duration because he stacks his CC. Or, he could exhaust and fight you, then pull you back in after you flash.
Instead of thinking about abilities, their applications, versatility, etc, you're basically just going "there's a tool in this game I'm not familiar with and I don't understand therefore the game is imbalanced" which is incredibly arrogant and self-righteous to be honest. Perhaps you should realize that this is a game you aren't familiar with and the idea that you have any understanding of how it is or should be balanced is sheer arrogance.