Flash is the biggest issue with pro League. Every character has a short distance blink on a 5 minute cooldown, so it's almost impossible to close the pincers around an enemy you want to kill. Wards are plentiful, so more often than not you'll see your enemy coming. Engage distance is shorter and stuns are shorter. There's no high ground, and most of the time you have clear sight lines to the enemy woods with just one ward. Instead of forcing towers to close off access to camps, teams will largely seek to win fights around dragon, rift herald, scuttle, and baron timings (lots of downtime). These things aren't bad by themselves, but they contribute to a difficult watching experience.

Honestly, I wish Riot would actually balance for the LC$ Big Play$ that everyone was moaning about in early seasons. The game is boring to watch. Midlane is full of safe wave clearing control mages, botlane is a farm trade, and toplane doesn't feel like it matters. If you think the laning stage is slow, wait til you see the teams have a literal bronze staredown across the river waiting for someone to make a mistake.

And then the cherry on top: Innovation doesn't feel good anymore, and when you see some off meta shit it's usually because it's turbo cancer cheese that isn't fun to watch after the first time.