This usually works unless you are fighting enemies with high speed/damage melee infantry, I tend to get overrun pretty hard by eldar when I do that, I try to get at least a couple squads of flayed ones when fighting eldar, necron warriors are a pretty solid counter to early game tau tho, and imperial guard. They struggle against chaos marines and space marines though... When fighting orks I tend to focus more heavily into flayed ones early as well if I can.
