I think legatus' has strong buff though from what I recall because his is a % increase, not a flat increase like Aelius has. But, with Legatus, you have to land 5 basic attacks vs Aelius' 3.
I wonder which will prove to be more powerful? From his kit, he might be a great diver because tanking turret hits will increase the damage from his fury'ed Q plus he can sort of jump back out with his E since the ult refreshes all his cds. Plus, he gets a shield from his W.
edit: its not specificly mentioned in the description, but does his ult have a CD? or is it purely based on having a set amount of fury? And if so, how much fury would be required to activate? If this is true, this results in Aelius being able to continually use his ult as long as he's able to secure kills.