I think it’s completely reasonable that the change will take time. I ran Developer Relations at my last company and my goodness…it took over two years to get our APIs into an improved state. So many complex things to consider (and engineering hated the idea of making a stable endpoint that couldn’t change!)
I do think smaller changes can happen over time and in a shorter time frame too, though. I admittedly have not looked into how your routes (or how routes in Ruby) are defined—but I assume some low-hanging fruit could be handled pretty easily. For example:
I can’t speak for everyone, but I feel like even having the endpoints exist in your current api spec—even if you didn’t have descriptions & examples, and even if the response model was fluid—would be a huge win. Simply knowing something exists is half the battle sometimes.