I backed it up with facts lol, you are now trying to say I don't know what I am talking about.
According to Ichifails you are silver, why are you even trying to argue about this.
Garen Q has a base of 130 at rank 5 + 140% of TOTAL AD. Garen builds Black Cleaver. That is hitting you after a DMP (Dead mans plate, because apparently we need to spell this out for you) auto slams into you, silences you with that Q that is hitting like a truck, maybe throw in a judgement for good measure, another auto, and then a villained R. Garen doesn't need to get you low for his ult to kill you, just below half.
Do some research on champion.gg and probuilds.net and realize no one is taking it because it's bad.