Where does it say that giving orders to a spirit uses a simple action? Not saying it's not in there, I just cant seem to find it.
At the very least, SR5, page 474, Combat Actions chart, Simple Actions category, 4th one down on the left side, "Command Spirit"
And don't forget that the spirit won't be able to act on any orders given until it can roll Initiative. A fast magician and a quick summons might be a spirit's detriment, and before the start of the next combat turn it could potentially be subject to Banishing and such.