Man, your point of view about reluctance is amazing, I agree with what you think about it. Its just that this way of thinking must be taken in a very cautious way, because in order to finish a game you *must* have a well defined scope, otherwise the chances are you never finish it because new ideas pop all the time. I talked about this on this old reddit post of mine. But I agree with you that sometimes it's good (and even needed) for the scope to change a little bit. I'll definetely change the levels if the jump is not good, thank you for sharing these great thoughts!
The tools I used to make this game are Phaser (TypeScript), Tiled (for the map), Piskel (for the art) and Beepbox (for the music and sfx). It's fully open source, you can check all the code here: https://github.com/diguifi/Dude-SideScroll
I'm at work right now, but I'm willing to play your game and answer your feedback post since when I saw it! Will play it soon and check your level design techniques! I'll also answer your post with some feedback :)
Yes, I do plan short maps, I plan a short game in general. It was supposed to be just a learning project (never used Phaser, nor TypeScript before) but it got so cool that I evolved the idea and started to make this game.
** MINOR SPOILER AHEAD **
I plan 2 boss encounters, but if you don't play the game "correctly" it will be only one boss.