You're premise is built on the exceptions. It does happen but it's rare.
I actually agree. So let's fold the idea of needing sailors with army experience and vice versa and post soldiers to the army, sailors to the navy and aviators to hotels, like god intended.
Right now that doesn't...
So not what Log, RCEME, Med, SIGs, ect do because reasons ?
The RCN is a bad example for your point. For RCN trades there are only two operational bases. And HPDs do not get assigned unless the person is part of the RCN. Those not wearing that cap badge do not get that protective blanket...
Just FYI a frigate has bunks for around 254 peeps. Of that about 30 pers are in the Log Dept.
Also when a ship deploys the crew is cut to bring on the com research, int, PAO, padre and NTOG. And that's not including staff if you're unlucky enough to be the command platform.
One to pay, feed and supply the ship.
You've left out Logistics
5 to 10 LT(s) HODs and a sundry of positions
5 CPO2 1 per department
I know what we do is seldom seen or appreciated so I will take every opportunity to make sure it is...