Real Talk: Why is League 5v5? Why Does Support Exist?
There is one obvious answer: to make ADCs viable. ADCs need damage sponges and CC cannons to keep them alive until they have the chance to redeem themselves after laning. Acknowledging this, let's move to the actual discussion.
If League were suddenly a 4v4 tomorrow, what is the role that would disappear immediately? The answer is, of course, support. ADCs would then be replaced because of that change, but that would take a day or two.
The question is, why does support exist? Riot's done everything in their power to make it an exciting, meaningful part of the League experience and despite this, it's still the most universally hated role. People dislike playing support. ADCs don't like relying on supports. Why? Because support is built from the ground up to be the least impactful role in the game. But they're still there. Why? Because there's nowhere else for them to go. They're literally the fifth wheel on the League experience. There are 4 inherent places on the map for a player to go - 3 lanes, and the jungle. They go bot because ADCs are horribly weak to everything from assassins to tanks (which is a recurring problem in league's balance philosophy).
I don't get it. If it were me, I'd make league a 4v4 tomorrow and rebalance champions accordingly. Most of the support champions can survive in other lanes anyway - at least, until they're nerfed in order to keep them from doing anything as a support, and killing them in any other role.
If the role were removed, the game would be better for it.