As I said, build Tanky through health or boots. Health is an important stay to be capable of tanking, and to take full effect of their percentage health healing
Garen does not heal whole fighting(except Conquerer which somehow stacks fully of E alone) and Ravenous Hunter
Garen is the second highest winrate Toplaner, and he has near 2 times the pickrate of 1st place ontop of countering 1st place.
Combined with on average loosing to only 6 toplane champs, while winning against 28 toplaners.
Second highest winrate, looses to 6 champs, from which 3 have really really low playrates, and wins against 28. 3 of which he looses against are ranged btw, and most of his loosing lanes range from 1 to 0.3% lose rate. While his wins average between 2 to 6% winning against opponents.
He needs nerfs in the sense that his loose rate against other toplaners is way, way too small, combined with his high winrate.