Garen's Spin deals less damage than before until level 16
New Garen: Physical Damage Per Spin: 15 / 18.8 / 22.5 / 26.3 / 30 (+ 34.5 / 35.3 / 36 / 36.8 / 37.5% AD) Old Garen: Total Physical Damage: 60 / 135 / 210 / 285 / 360 (+ 210 / 240 / 270 / 300 / 330% AD)
E gets maxed at level 9, so let's see the numbers. Assume that Garen has 200 AD. At level 9, Garen has 7 spins. New Garen: (30+.375 x 200) x 7=(30+75) x 7=735 Old Garen: 360+3.3 x 200=360+660=1020
Let's look at level 15, assume 200 AD, with 9 spins. New Garen: (30+.375 x 200) x 9=105 x 9=945 Old Garen: Same as above=1020
Level 16, 200 AD, 10 spins. New Garen: 105 x 10=1050 Old Garen: 1020
Clearly, Garen does much less damage than before. Now if the target is isolated, the damage goes up by 33%. But how often do you get your target isolated? I hardly ever get my target isolated, and they are isolated for less than 1 second.
Assume Garen gets his target isolated, and they are the villain. Assume the target has 2000 hp. Then at level 16, New Garen: (105 x 10) x 1.33+0.1 x 2000=1396.5+200=1596.5
So the maximum potential damage that Garen can unleash is 1600 damage with his spin. But realistically, he doesn't isolate the target, and instead does 105 x 10+.1 x 2000= 1250 damage to the villain.
My point is that New Garen is much weaker than old Garen until level 16. In terms of numbers, [(30+37.5%AD) x X] is always less than 360+330%AD until X equals 10, where X is the number of spins.

before his rework, this was easily done. You didn't need the villain mechanic to shut down fed targets. It's actually harder to do the same thing currently pre-16.