You're right. Weapon balance will need to be reworked in the future when there's more content in the game. I definitely want you to feel the progression from worst guns to better guns, but i cant make it so it's too easy when you have the good guns.
Game is still too easy on hard difficulties, i'm gonna have to add some crazy abilities to the zombies to make it harder.
Also, it will all depend on the difficulty balance of the boss fights, the grinding to unlock new weapons and the variable difficulty system that will be coming on 0.6. It's still too early to judge the balance of the weapons, because the gameplay loop is still nothing like it's supposed to be in it's final version.