Thanks for playing and glad you liked it.
We designed the unlockable weapons to be side-grades as opposed to upgrades, with no one weapon being objectively better than another. At least that was the intention.
As for difficulty, we send stronger enemies at the player the farther in you get. Have you found the laser pointer in the options menu? That thing really helps when you are learning the game (and when you're just playing it, both me and my co-dev can't play without anymore).