Something that might give Garen teamwork potential

Changing his W to be able to cast on allies, with the added tenacity I'd like to venture a bit further and say it could scale by 20% (tenacity) & 12.5% (damage reduction) per nearby enemy champ.

In a 5v5 garen has a PRE EMPTIVE QSS (have to use it before getting hit by CC) and damage reduction he can use on himself or an ally, while laning this will not be the case, keeping his laning in check while actually giving him some team fight tools.

The way he does damage is another issue but this is a nice start.