I like how they nerfed TP because it was being used to much.

Read up on it's full history before you bash Riot's position on it. No it hasn't been nerfed, but it's also not true that Riot's never tried to nerf it.

TP is hardly even nerfed if you asked me. You can literally reduce summoner CD by 40% now + Summoners Insight (which is pretty accessible to everyone now)

Flash isn't mandatory in every role and it hasn't gone completely untouched since forever. Just in preseason 2014, Riot halved the range on Flash. That's right. Before last year, the range on that spell was double what it is now. And flash is so vital because it's an easy escape. Do I feel like they need to just rework the entire system altogether? Yeah, I kinda do because there isn't much by way of diversity right now. Flash isn't mandatory on every champion, shall we say. Shaco jungle will always run ignite/smite, and why? Because ignite/smite is more useful that flash/smite on him. Singed top? TP/Ghost. Some ADCs will run heal/ignite, and some mid laners can choose to run tp/ignite over tp/flash. There are a ton of examples of champions who flash is just plain bad on. You only say it's mandatory on everybody because the people that it is used on are popular.

Unlike Teleport, impactfully nerfing or removing Flash would literally upend the game. If you think this preseason is bad, you'd have one FAR worse if they up and removed Flash. It's too important to the game balance to just be pulled out.

If they wanted to make Flash not omnipresent as a summoner spell without screwing things up too much, the best they could do would be to make it an active on boots or something, with the same CD and everything.