How does Mapbox stack up against what you've built? Does Mapbox provide any advantages or is are the two not very comparable? How difficult would it be to spin up a Mapbox competitor?
How difficult would it be to build a competitor to Mapbox? Well, if all you care about are map tiles, it's no big deal. If you want to build a business around it, that's always work. You're going to need to build the tiles, have infrastructure to serve it, monitoring, staff to manage it, billing and charging infrastructure, etc...