So atm Garen ult cannot be flashed out of, and if Garen loses vision of his target while casting his ult; they still get hit anyway. This was not always the case.
Skarner ult, on the other hand gets canceled if he loses vision of his target. It's really annoying when I'm in the middle of casting ult, and the enemy enters a bush (or Akali hits W) and Skarner ult gets canceled.
And anyone who plays Skarner(do you exist?) knows the moment you hear the "click" sound on your ult, you immediately start walking backwards into your team. So essentially, if the enemy cancels your ult you're fucked. It's hard enough being a champion without gap closers in a meta filled with CertainlyT-esq champions.
Balance-wise Skarner already has a low playrate and winrate. This small buff to his ult is not really going to make him OP, or change his power much at all. It's just going to make him **slightly** more consistent.