TL;DR: I don't agree with you. You are using too basic physics to describe these phenomena. I suggest alternatives.
I don't quite agree with you on this one at all. You can explain the great abilities that these champions have with 17th century physics. You need some frontiers of physics here. And these are just ideas on top of my mind.
For Sona: I don't think that the sound wave is travelling that slow. I think this is more of a sonoluminescence effect (but in air which would suggest huge energy of the soundwave). And based on the properties of the atmosphere it just takes some time for the light to fade, hence making it look like the sound is moving slow. Wiki sonoluminescence: What causes the emission of short bursts of light from imploding bubbles in a liquid when excited by sound? It is a very strange physics effect and a great physics problem. But it is very beautiful so look it up.
For Soraka: If you assume that Soraka has access to some unknown source of energy her magic can be to actually create matter from energy hence creating a falling star. (If it is just a normal star orbiting their galaxy such fast change in momentum would collapse it into a black whole / tear it apart). Another variation of pretty much the same idea is that particles "spawn" and annihilate in space-time all the time. So Soraka may have the ability to control that effect to spawn a star (or multiple stars) given that the mean energy of free space stays the same. In other words she spawns a star at a specific point and overall the whole universe gains this much extra antimatter (which is not that huge of an effect given how matter dominated our universe is).
For Ashe: It looks like the arrow simply has no friction or it seems like it has no friction. Assuming that it doesn't have external forces acting on it after it is shot it should have no friction. And there is an effect like that in nature. It is a super cooled fluid and a similar effect can be observed for supper cooled liquid helium. So pretty much Ashes ability would be to super cool the gas out of the atmosphere around her and give it initial momentum (other interpretations can be more sensible, but this is just on top of my head).
Thanks for reading.