Thanks for playing through the game! As mentioned in the tutorial for the butterfly, it is possible to beat the entire game without it, so that is indeed intentional. At this point, I have plans for 3 more Worlds if the game gets support from players.
EDIT; I should mention, most of the difficulty in the game comes from trying to beat it in record time (my best time is around 9 minutes), so I don't plan on making the base game any more difficult because I'd like to stick to the idea of being accessible enough that anyone can finish it, but I did have the idea to make extra-hard levels as a bonus to players who support the game.