Garen feels a bit odd right now

Very little upfront power so you get out-dueled or forced out of lane early, then you hit level five with your spin2win and use your massive mvspd + regen to be everywhere and kill everyone.

I'd like to see his early game buffed and his mid-later game nerfed so he stops dominating with utterly absurd map control, and to see increased viability in alternative build paths or options.

No, 'making him less sticky' is a terrible idea because playing a champion that will never be able to get into contact with anything means he will never get played, as we've seen demonstrated in the past.

Buff his flat q + e damage, tweak the ad scaling on his e to be consistent (80%), alter critical strikes to be 'full' damage, scale the # of hits to his attack speed to make full crit/attack speed jungle builds more viable and to make players more willing to pick up ghostblade (speed up that spin).

Change villain to give a garen who kills the villain to restore 3% hp, mvspd, and a tenacity boost (nonstacking) - rewarding them for being successful in it, not punishing the person for doing well.

I think that would cure the problems of him killing and doing absurd amounts of damage while building generally full tank, picking up his early game slightly, and making different ways of tackling the more interesting.