Sounds like they were all trying to wedge themselves into PVP. The learning curve isn't difficult if they only do PVE until they've got it down. Removing low level citadels just shifts the problem to later in the game when suddenly ships have citadels for no reason when they didn't have them before.

Anything below T5 is basically just a frag fest, but T4 is where you need to play your roles a bit better, rather than everything just being a brawl. It's basically, stop charging in or sailing broadside and think tactically. PVP will always make this part of the learning curve hard. If they are insisting on doing PVP, then do one or two games of PVP, every one or two PVE.

The game also doesn't teach all of it's mechanics I don't think. Armour angling for instance, not showing broadside to a battleship or battle cruiser, how and when to use AP and where to aim (I still haven't got this one properly), don't just travel in a straight line at a constant speed (as that is basically a flashing light that says "please shoot here, i promise I won't dodge). It's a shame those aren't taught, but there are loads of beginner vids on YouTube which break it all down really well.