These are some of the builds I use when I have new players or two many AI crews.
1. Blenderfish
Its a ship that has the one gun. No need to get bifectas or trifectas. The gunner stays on the front gun, and engineers need just enough awareness for the flamethrower.
2. Long-range Mobula
Mobula has five light guns, all facing the same way. I can have five different guns (I run flak, hades, merc, artemis, banshee) and give the entire crew a training camp on aiming. The only downside is that a Mobula cannot possibly be repaired by new players, as they won't even know where all the components are. The captain needs to keep the ship safe, possibly without damaging piloting tools.
3. Metamidion
Just like you've said. It's an easy and debatably OP ship. Everyone has a set role. Metamidion teaches a whole lot about the game including but not limited to: coordination, piercing damage, explosive damage, simple parkours, and engine maintenance. However, you need to have three attentive crews, or the ship does not function. One AI can also ruin your day.
4. Hwacha Galleon
You'll need at least one experienced engineer. Stick your powder monkey in the bottom deck (he'll love the hwacha), tell your newbie engineer to fix what you tell them to, and have the experienced engineer on the top deck. The two hwachas mean that gunner has a room for mistakes, the massive health pool means engineer has a room for mistakes. But beware, the low mobility means that pilot has little room for mistakes.
These are the ships I use to teach the ropes. I've mostly had a good time with these, except that one time...