Writing game engines is a blast, but they're the ultimate in feature creep/nerd sniping. You'll spend all your time building the engine rather than focusing on gameplay.
But I also think that for most small games (1-2 developers) it can also a be a good idea not to use an off the shelf engine either.
Write the absolutely minimum that you can get away with to achieve the gameplay and look you want to achieve. Hard code everything for your specific game.
It's true that if you want to write an engine you can distract yourself from focusing on gameplay. But I think you can actually fall into the same trap using an off the shelf engine too. You end up spending a pile of time learning and working with the advanced tools and not focusing on gameplay either!
The basic rendering APIs are actually not that hard to use if you forget about generalising everything for some future that never arrives, and there is a hell of a lot to be said for working on a code base that one person entirely understands. The development speed benefits of this should not be underestimated.
Game site: https://papadar.itch.io/eatvolve
Playthrough of an older version here: https://www.youtube.com/watch?v=s9JgvTus0O0
GameMaker Studio: https://www.yoyogames.com/gamemaker
https://github.com/dungeons-of-moria/umoria/blob/master/READ...
For the kind of game presented in the article, Gamemaker Studio would be more reasonable. Unity has a lot you don't need, which obscures the path to making something simpler like this.
I'm sure there are other good options too. I think there's a JS-based platformer-oriented engine out there.
Out of curiosity, why do you bother writing a statement like this? Is it to assuage your ego? If you haven't done game development before, it's safe to assume there are gaps in your knowledge and you're better off admitting it outright.
I'm relatively confident with programming in general, but I don't know where to start with something like this. Did he use an existing engine or framework like Unity? Is that the best place to start game development?
This game looks amazing and I'd like to try to draw some inspiration from it.