Working in the auto salvage pool business (bikes too)…You wouldn’t believe how many bikes we get in with 7-50 miles on them. Seems like every year there is at least 1 250 Ninja amongst others (popular starter bike). A couple of years ago we got a new H-D in that the guy crashed in to the curb leaving Spitzies (maiden voyage).
My point is that learning in the dirt on a less expensive bike IMHO is definitely the way to go. Everything you learn in the dirt will carry over to pavement in one way or another. Then stepping up in increments to a more powerful bike for the street isn’t a bad idea either.