Deep Rock Galactic

I started playing at the weekend with my teenagers, we've agreed to only play DRG when we're together so no-one goes off ranking up too fast which is what happened when we played Valorant.

We've selected classes somewhat randomly, I'm playing engineer, they are driller and gunner.

After about 3 or 4 missions they've got to rank 4 and I'm still on 3. I feel like they're getting more kills because they have more killy weapons (waaagh), is that what the rank system is based on?

If so, have I chosen a class which is slower going or gets better late game? Or, does it not really matter as much as I think? I can see that ranking up means better upgrades, presumably therefore more kills so it could be a feedback loop.

Overall we've found it to be great fun as well as a kind of chaotic, screaming mess!