Can Alistar's bonus Attack Damage from his ult be replaced with more visible and Support-like power?

(even if that power might be a nerf in certain situations)

Unbreakable Will

• (NEW) Passive: Alistar marks enemy champions for 4 seconds who apply crowd control effects on him (half duration for slows). He gains 6/9/12% Movement Speed when walking towards them.
• Active: Alistar removes all hostile crowd control effects from himself and takes 70% reduced damage for 7 seconds. Additionally, he gains 60/75/90 bonus Attack Damage --> his basic attacks against marked enemies consume the mark to deal (75% base Attack Damage) as bonus physical damage on hit, slow the target by 15% for 2/3/4 seconds and reduce their Armor and Magic Resistance by 15/20/25% for 4 seconds.

Alistar likes Movement Speed for engaging, and although the Attack Damage would offer more raw and reliable power, this effect allows his team to deal more damage, too.
The 15% slow for 4 seconds wouldn't be all that strong in most cases. Alistar has no other slows so any other form from his allies would simply override it (as only the strongest slow is applied). The bonus Movement Speed equals about 20/30/40 flat Movement Speed.