Dear kantieno,
The Weapon Master medal only unlocks if the last weapon is a collectable weapon. If you collect all weapons possible and then craft Shadow's Edge the variable for having all weapons won't trigger. This problem might have been the same for the removed Lotsa Weapons medal.
About the game: Nice adventure. Fighting enemies were much easier than avoiding projectiles/obstacles, but I prefer it that way as I am much better at hop and bop platformers than combat games.