FWIW, I don't like spell overlap and have eliminated it completely from my Fatebinder system. There is no spell sharing. Classes may have spells that do similar things, but there are always significant differences that reflect the nature of each class.But lots of classes have spells. Some classes use spells in a slightly different way, but lots of them use the same spells. Why should combat maneuvers be any different?
But a level 5 rogue in 5e will have +5d6 sneak attack
Is that confirmed (i've only seen up to 3rd level characters so far)?
So, for negating oncoming damage, do you have to save dice?
At some point, it was scaling like that yes.
I find it best not to assume (people get fired that way); are we talking about a 13th level Rogue doing 13d6 SA damage?
It could well be that you need to use cs dice for your secondary attacks, or that secondary attacks are dailies (i.e. fighter surges)I'm concerned about the power inflation that this mechanic might bring. They've said that fighters will be getting extra attacks as they go up in level, and now they're getting combat superiority dice on top of that? This means fighters will be able to put out ridiculous amounts of damage. Hopefully, this mechanic replaces the extra attacks fighters were going to get rather than adding on top of it. Even then, I'm still a bit concerned.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.