A year is nothing in the grand scheme of things. If you can't invest a year into building tools that could be your foundation for the next 3 decades, then what you are building is just a quick-rich scheme that doesn't matter. Use whatever you want because it doesn't matter...and your game probably isn't going to sell anyway. Those are the odds.

But as they've pointed out, you kind of need to know that stuff anyway, so it's time well spent.

I don't have a ton of gamedev experience, but at least graphically that game isn't doing anything you can't do in a few hundred lines of C++. Maybe that's part of their problem. Why use Java if you want to make a mobile game and it isn't well supported on one of your primary platforms? That sounds like a bad fit.

Unity and Unreal are super cool but they are also bloated with features that you don't need and lacking in others you do. For the longest Unity required you to use 3rd party modules for a camera. A camera....something that takes a few lines of code for a basic implementation. Why didn't that come standard?

If you really want to hurry to market yet another game by all means use one of the existing engines. It might even work really well. But if you want to do anything interesting, you're gonna be doing custom stuff anyway.