Looking back would it have been easier to do the whole things in JS/HTML/CSS?
Not at all! This is a mobile game and getting 60 FPS on mobile in a browser is not trivial, even with graphics as simple as these. But natively? Ridiculously easy.
The game is simple/hard and beautiful.
I am just curious. What engine and development tools did you use?
If I like a game, I want to know the backend tools that was used for developing.