I'm just going to quote my other post on here.
{quoted}
He hasn't had a meaningful change in ages, and has had his power in a vacuum lowered a bit by certain item changes.
He is almost exactly the same as he was when he last had a 49% win rate. The only difference now is the number of people playing champions that are inherently weak to Garen compared to the number of people playing champions that are inherently strong against Garen.
Garen is still just as weak to his counters, people are just not playing them anymore.
There is absolutely no way Garen will become dominant, unless the meta somehow prevents all of his counters from being viable. This spike in win rate Garen is experiencing is fully due to the play rate of champions that Garen does well against going up, and has nothing to do with Garen's strength itself.
Just play one of his counters and don't make obvious mistakes that a skilled Garen can capitalize off of.