Does anyone actually find safe towerdiving fun?
Towerdiving works as a mechanic because it's supposed to be risky. The diver goes into a very dangerous area to try to secure a kill, knowing that they are taking a major risk and can easily be outplayed and die instead.
But when the champions doing the tower-diving are tanky enough to just withstand the tower shots almost indefinitely, then the risk is gone. They can just walk under the tower, eat several seconds of CC and not care, kill 1 or 2 of the champions under the tower, and walk out safely. There's almost no risk, little chance for either side to outplay each other and show their skill. Just a terrible experience for the laners being dived without recourse. Even if they see the diver coming through wards, there's nothing that they can actually do (other than maybe outright abandoning their tower.)
Does anyone actually consider the latter form of towerdiving fun? And, if not, why is it still in the game?
Yes, your R just make you more brainless and will save you from your mistakes, so you can towerdive
