Its not too different from what you are doing right now, but since its server side, you get to call all the methods directly without all this HTTP/networking garbage complicating things. Which also has the benefit of sending less chaff over the network.
Not only would I use Epicor functions, but then if I did have to call the 1 or 2 Epicor functions I made, I would use the RestHelper library instead of reinventing the wheel.
I’m not sure it would take too long to switch as you would be mostly just translating your Rest calls into direct BO calls. It might be worth looking at before you finish this project.