Can we please make immobile casters who rely on skill shots viable again?

There is way too much mobility in the game for these champions to function. The only one that's actually usable right now is Xerath, and that's only because his skill shots are significantly faster/wider than everyone else's.

I can't even play Vel'koz anymore, because anyone at a Diamond level can trivially avoid my entire kit thanks to the abundance of movement speed and dashes/jumps.

Alternatively, even if they fuck up and are going to get hit, they can just flash over my entire insanely telegraphed kit, and then auto me to death while there's nothing I can do to stop it.

Looking at LCS picks makes it pretty clear that this is a major issue. The top picks' skill shots are all unavoidably fast and/or they have targeted CC to ensure it lands: Ryze, Azir, Orianna, Taliyah, etc.

One possible solution would be to scale the speed slightly with level, so they keep up with movement speed.