Ideas and suggestions.

The main advantage of TP over the discussed options is that it teleports the hero. Transferring troops as artifacts is cool for breaking through with mages, but it doesn't really enhance the hero's mobility. Unless it's done according to the scheme: "gave troops - got destroyed - bought back." Therefore, the level is definitely not 4th, it's more like 3rd, which is optimal. It also provides low-level control, which is good in itself. I'd also like to note that this spell doesn't necessarily need to be upgraded for the hero; it's quite possible to manage with having it available for mages. I don't know if that's good or bad. If it's bad, then you could allow teleportation in only one direction on the map (for example, "to yourself"), and require an advanced element for teleportation "from yourself."