I'd give Aether a B honestly. Far too low of a proc rate to be relied on; it basically just exacerbates Sol's already-unreliable healing based on enemy hp by another order of magnitude. Yes, it's good damage when it goes off, but you really need rightful king to make this skill worth ANYTHING; on its own it's pretty lackluster.
Paragon I would give an S. It is the defining skill for mid-lategame grinding; veteran comes earlier and has a huge boost due to early availability, but Paragon makes grinding tons of Spotpass units up much faster. I do a LOT of spotpass unit grinding - gotta catch em all bro - so Paragon is worth more to me than it would be if I were worried about L+ chap 1-4 stuff.
Another day, another unsuccessful genetic abomination!
I don't understand people's logic in giving Aether lowish grades. Comparing it to Sol? Let's be honest, there are 2 characters in the game who aren't spotpass/DLC characters that can have both at the same time.
The first being Lucina and ONLY IF MU is her mother which a lot of times is a waste because as people say, she has Rightful King to go with Aether. I guess if you really want the healing effect more often you could -technically- replace Aether for Sol, but I doubt many would do that. The second, Morgan who is good either way but you waste Male MU's gene and ability to make another character Morgan.
Now like I said earlier, if your character has this ability, it's more than likely a fact unless they are playing support role, that they are going to use this ability. How does anyone give an ability that they WILL use if they have in almost all situations worth less than S rank?
Sol and Galeforce are abilities some may not consider using, but they are amazing and will usually end up being in a characters set if a character has access to them.
Yes Aether has a fairly low activation rate, doesn't change the fact that if your character has the skill, you will most likely run the skill.
But I'm probably just wasting my time explaining all this since most people are too stupid to think of anything besides activation rates and comparing it to skills that the characters likely won't have access to. That and majority of posters won't both reading others explanation of things before giving their rating.