The most important thing in the first three years is that the child be cared for, for the majority or the time, by someone who loves them and has a stake in their development. Harry fits that bill perfectly. In the cases of royal children, often the long time nanny fits the bill too. The biggest issue is when the mother gets jealous of the attachment to the nanny and fires them. It is reported that is why Diana fired the nanny that cared for the boys, or at least William, as a baby baby. Assuming Harry and Meghan keep the same nanny, that will be good for Archie, especially if they plan to both be away a lot.
William and Kate seems to have clicked well with their nanny and there has been no reported issues of jealousy even though I am sure the kids are very attached to her. Kate also seems to be very hands on and enjoys doing the everyday mom stuff.