Is it normal that the amount of experience needed to level up is not the same between the pyromancer and the pirate class?

I am currently playing Hero Siege in Multiplayer Local and we face an issue. The Pyromancer's level is different than the Pirate's level.

• We start the game at level 1 together.
• We play strictly together.
• The Pirate does not seem to own an item to increase experience gain.
• We note the cap around the level 30~.
• The difference increases at each level.
• We mostly don't die.
• We play in Nightmare.
• We play on Steam.
• Steam says the the game is updated.

Current level:

The Pirate's cap to the level 39 is 50.3k.

The Pyromancer's cap to the level 35 is 74k.

The problem is troublesome because we find more and more items cap for the level 37 and higher. The pyromancer starts to be out of league. Is it a normal behavior? What can we do to mitigate this.

Note that I copy/paste this question on steam. I will update this post if I get an update there.