Hi hi,
It's been a while since I did a proper champion concept analysis, so if I miss something, mb xD
Just a general rule of thumb when creating concepts:
The more "tools" a champion has, the more counters they should have.
Tools can mean things from high dmg, low cd, lots of aoe, to even mobility or even just survivability.
Just something to keep in mind when creating concepts, cuz I know although some abilities might seem cool af when you come up with it, it might not be the best for this particular champ.
Okay let's start with the image you have in mind for this concept.
Do you want a tank shredder? one that can rip through both armor and mr with ease? If yes then he mustn't have too much threats on non-tanks, but he also needs a way to keep him alive against non-tanks so he can actually do his job. Something like "Aidan heals for x% if the bonus magic damage he deals to units who have their defense shredded" can do wonders.
Or do you want a simple hybrid carry that's more aoe focused than Jax? If that's the image you have, I strongly suggest to change his w for something more fitting of a skirmisher/duelist. There are a lot of options, such as becoming untargetable, increased ms and bonus effects for aa, or even something like throwing away his staff, creating some sort of field (shen style, if you will).
Overall, I think one of the most important part of a champion is the fact that you will be able to achieve something if you main it.
For example, by even maining garen you will be able to w at the right time, avoiding the maximum amount of damage.
by maining blitz you will get a better idea of how you can "combo", like q aa e, which is absolutely legit but no one does it xD.
My point is that for Aidan, there really isn't much to master. Sure, someone who mains him knows which walls he can jump over, but that's about it. Changing some abilities into skill shots can help, or just make the kit more complicated will do the job as just well.
Lastly, just a personal note...
Since he is the Wielder of True Flame, shouldn't he have more things to do with flame or at least true damage? I mean a caster/bruiser would definitely be interesting, or even just a melee caster (not melee ap bruiser, big difference) isn't a theme that's often touched on.
Hope this is alright ;)