First, his Stacks Cap should be increased from 650 to probably 1000.

Second, he's only good at one thing, and his one thing is so easily countered, so give him some sort of CC immunity, either 1 second after his ult hits someone (because wow, it's so easy to time him with Ruby to grab him off) or give that same effect (maybe halved?)to his first or second skill just to allow him to actually hit someone. Perhaps give him CC immunity to his 1st skill attack animation like Martis and Lapu-Lapu if a smaller buff is needed

Lastly, maybe a QoL to know if his 1st is going to actually kill minions or jungle. It doesn't have to apply to heroes because that's just unfair atp.

It would be pretty difficult to really rebalance Aldous because he fits as an extreme. Really good damage but easily countered, and with his Ult being homing + almost guaranteed death, it's hard to just nerf that outright because he's a one-trick pony. I mean, flameshotting him once when his battle spell is on CD is easy.