(fires Irelia's ultimate into entire enemy team, heals virtually nothing) Well, that was expected...
You could have a Spirit Visage and complete build, and Irelia's ultimate wouldn't even heal 300 health if you got 5 Champion hits with all four shots. Why? Because ARMOR.
Riot, stop making it a traptastic ultimate. If it's not going to heal adequately even in its best-case scenario, it shouldn't heal at all. Please look at making Transcendent Blades heal flat numbers (like Renekton's recent Q change) instead of being based off the damage she deals with it.
If you refuse to make this change, you are making it ANTIFUN FOR THE PLAYER.
EDIT: Since values are probably needed...
Heal per minion/monster hit: 6/8/10 (+0.05 bonus AD) (+0.025 AP) Heal per Champion hit: 20/30/40 (+0.15 bonus AD) (+0.1 AP)
(these numbers are only theoretical; don't freak out)