You absolutely do not have to use a controller. Both input methods are equal and you should just use whatever you're used to. That being said, on PC I recommend people set lock-on to toggle, and set targeting to camera for both options rather than auto or whatever the default is.
As for aiming the abilities, well, that's part of the game. Nothing is a skillshot with the level of skill ceiling as battlerite, but that's necessary for the game to be playable on a limited device like a controller. When you're locked on to an enemy, the default location of an ability will be at their feet. This will let you quickly throw an ability like gizmos bomb at your enemy and be able to manually adjust it to where you want. A tap is just dead on your target, and holding it will allow for a quick adjustment if neccesary. Sometimes for an ability like kulev's totem or zero's wall it makes more sense to remove lock-on first so your ability isn't going directly to the enemy.
As for the 60 fps cap, it's already been announced as a plan. The game will always internally function as a 60 fps game (think of it as a tickrate of 60), but on a capable pc it will render at a higher rate for a smoother image. This will allow pc players to play like we're used to playing but not provide a competitive advantage over console players which is important to maintain competitive integrity. We'll still have input at 120hz+, but my understanding is that we'll essentially be seeing interpolated frames rather than having an actual latency advantage. It'll definitely make everything look nicer and make the mouse input feel even better though.