So, a couple of thoughts,
The list is technically legal but you can’t run a RoW with it as Orth does not have master of the legion.
The main advantage of running CoBi is that you don’t have to take tacticals in your troops slots. Tacticals are reasonable objective holders, I find them most useful in rhinos. But for an additional 35 points per squad you can take veterans, so if you really want to take 10 man marine squads in rhinos and your troops slots are filled with immortals, I’d find the points to upgrade them to vets.
It’s worth looking at your Meduson sergeant load outs. Breaching charges are pretty useless in my experience, there’s a 50% change it will flip back onto your squad vs most opponents, and when you’ve loaded up your sergeant with kit, that’s a lot of wasted points. Perhaps you could argue it’s worthwhile on a “bare bones” sergeant, where the risk of loss is slightly less, but generally I don’t ever find a use for them. Taking power gloves and meltabombs is something to consider, there is some value in taking both, but generally I will take a power axe and a MB or a power glove, personal taste I suppose, but potential for points stripping if needed.
With regard to your Gorgons, lightning claws aren’t a great option as they have base initiative 3. So they will be striking after regular marines regardless, the additional shred rule really doesn’t make up the deficiencies of I3 and AP3. Anti-tank is something that the list lacks, and perhaps more specifically, the ability to take down walkers (ie leviathans). If you take the Gorgons, I would be loading up on chainfists (x4) and a grav gun to go vehicle hunting. With this load out, they will make up for the deficiencies of your immortals (avoid CC with walkers with immortals).
I think a single rapier battery is of arguable value, I would use the points elsewhere. The same could be said about the predators, their removal from the list could make way for some more AT
focused units. Or, if you like preds, upgrade them to use lascannon sponsons and squadron them.
Regarding the Medusa battery, I’m not sure how many tanks you were thinking or running? I like Medusa’s, my fear with them these days is their vulnerability to alpha strikes. The more recent inclusions of Terrax drills and boreas missiles on deredeos make me think Medusa’s are more of a liability these days. They have weak side armour, they are squadroned and they are a significant threat, which makes them a prime and potentially easy target. It might be worth considering a pair of Scorpius whirlwinds. The issue with them has always been the efficient use of HS slots, but they have better front and side AV, just something to consider, as their inclusion will depend on how many HS slots you have left.
Reworking your HQ should probably be considered. Autek Morr is worth a look at, he could potentially give two units PE, make his own unit fearless, give you access to castellax in your heavy support and give your units significant durable AP2 close combat support. He’s expensive, but he brings a lot to the table.
Finally, it may be worth getting at least some anti-air cover at 2500, unless your meta doesn’t use flyers all that much.
I like the principle of using a stormlord, just be aware of its vulnerability and the effects it’s destruction will have on the passengers.