R Olaf instantly removes all crowd control effects from himself and block the next 3 incoming crowd controls (not the damage) effects and he is immune to permanent crowd controls effects (field slows,ashe's q) until he blocks the next 3 incoming crowd controls .Additionally he gains a movement speed bonus for 1 second when moving towards enemy champions. During this time, he loses the passive bonus but gains bonus attack damage.
If they ever do that they must compensation buffs (because olaf is non-mobile champion because of his Ultimate that blocking infinity cc for 6 seconds), utility buffs or mobility buffs.
Option 1 (utility-power/peel-power)
Rework his q: q gains one additional effect: Olaf's axe stun his target for 1 or 0,8 seconds .Olaf cant apply this effect at the same target for 8 seconds
Option 2 (mobility power /duelist power) the best at my opinion, because olaf mains want him as duelist
Rework his e : e gains one additional effect : when Olaf use his e he blinks behind target. Now his w makes sense because he can stick to the target. He is not unccable anymore at teamfights, so we can put him some mobility. Most supportive champions that are based on CCs have 3 or more ccs. Also a short range gap-closer supposed to be spamable (Imagine if vaynes q had big cooldown)
(Sry for my english)
as long as he doesn't have flash up these are your best bets for slowing him down