Sachen 3.5/5
This thing costs one point and it comes with a defender fighter. Cheap spam unit if you want to bury the enemy in fighters, its also not that bad at dealing damage in a wolf pac since if you use them odds are you might have 6-12 of them. Very good in era 3, a bit weaker in era 4+ due to Coronas turning up. Originally appeared in Crackens Threat Dossier in the old D6 RPG. Role carrier.
Marauder Corvette 1/5
Why you would build this over an X Wing or E wing at over 3 times the price is beyond me. Avoid. Role fire support (weak)
MC 40A 3/5
I thought this ship was pants because it costs 3 points and its not a strike cruiser. However it is very very good at chewing through shields due to Ion Cannons and Missiles and qualifies as a mon cal ship so you can build it cheap on Mon Calamari. Very useful in the early eras when you build mon call fleets that are two tanky to die. Comes with a free B-Wing. Role fire support.
Corona 5/5
This ship replaces the Nebulon B frigate in Era 4 (I think). It seems to deal a bit more damage but it spits out 2 E-Wings instead of X-Wings and they are better. For the fleet points though you could have 2 Nebulon B and 4 X-Wings instead but you no longer have a choice and X-Wing spam is kinda boring anyway. Deals enough damage to mop up ships or have a crack at AI derp fleets that love charging past your front line. Originally appeared in Crackens Threat Dossier for the old D6 RPG (which I own). Role carrier.
MC 80 3/5
The MC80 technically counts as a capital ship but costs 4 points like a cruiser. It deals an anaemic amount of damage as it only has 4 turbolasers and a couple of ion cannons but it can take a beating. And it carries a X,Y and A wing. Since most NR ships carry great fighters your lack of firepower mostly does''t matter. You can more or less copy the Imperial fleet template (4 ISDs, 5 VSD's etc) replacing ISDs with MC 80'b's. replace the VSDs with these and fill it out with a few MC80A's and Nebulon B's. Imperial and Warlord ships more or less run out of shields, the X-Wings clean up and your shields can soak the imperial damage all day long it seems. Have fun not losing any ships, that is what Bothan Assault cruisers are for. Role Capital/Cruiser.
First I would like to make a point about the MC80A. When you say it only has 4 turbolasers that's very misleading. It has 4 hardpoints that shoot 5 pulses per burst so it effectively has 20 turbolasers.
As for ratings, I feel you have Corona, Sacheen, and Mc40 too high and Marauder too low.
Corona does not deal more damage than a Nebulon (they both suck at that). Both of them have 4 effective turbolasers. Corona has one ion cannon, just one. Corona has 10 laser cannons and nebulon has 12 so both are about half a corvette in flak support. Corona is fine as a carrier but since it costs 2 pop instead of one I would not put it at the same rank as the Nebulon which it ironically is supposed to replace.
Sacheen is ok but 3.5 seems too high of a rating for me. I would say more like 2.5. It is interesting that you say they deal good damage because they only have 5 turbolasers and 2 ion cannons and 4 laser cannons.
Mc40 is in an awkward place at 3 pop. With only 4 turbolasers and 10 missiles that take forever to recharge, they are pretty junk once shields are down. 10 ion cannons are nice but yeah, big damage problems after shields are gone. They are also really fragile unlike the other mon cal ships. These are worse than Vic-I's which makes sense since they are cheaper but 4 of these will lose to 3 Vic-I's handily. I still use them but not a whole lot, and I would say they are below average.
And now the Marauder which I think you really underestimate. The Marauder has two weaknesses, one is a shorter firing range which requires you to micromanage the unit or else it is likely to just sit there doing nothing. Two is that it is paper thin which is a bad combo with poor range. However, it is only 1 pop, carries an x-wing, and has 24 turbolasers. Yes, 24. That is more than an MC80A (no ion cannons but still). You say that Sacheens are decent in a wolfpack? Try sneaking a few marauders around and watch them wreck things. 24 turbolasers on a pop 1 unit is absolutely nuts. I usually bring 4-5 of these in my fleets and once the ai is wasting their time shooting my mon-cal whales you move the Marauders in. If this thing had 2100 range like everything else I would maybe give it 5/5. As it is though they are hard to use and are prone to dying so I would say 2.5 or 3. Ironically one of your best damaging ships in the early era NR.