Grenadiers are faster then any t1 vehicle and shoot further then any t1 vehicle, therefor they kill them all. Bomber can be scary but with just a few spinners in the mix its no problem at all anymore. Dox and boombots can be used effectively against just grenadiers (still takes some skill) but with a few ants, dox and infernos in a mix thats heavy on the grenadiers, you kill all t1 compositions i think. I'd say grenadiers are as overpowered as how well you micro them. The better your apm and micro, the more grenadiers you should use.