I wouldn’t say they’re relying on it for operations. It’s not like they doing some internet controlled submersible, it is still watercraft with someone at the helm and more than likely, they use some type of local communication for the surface crew to communicate with the expedition crew.

One data point from me: it's not unreliable.

Likewise for me. However, I'm on land, where the Starlink satellites don't have to relay comms between each other. It's a completely different story out in the middle of the ocean. Starlink only recently started their laser-based relay system, and I have not heard reports about its reliability. It might work great, I don't know. I do know that it was a difficult engineering problem to solve.

What better alternatives would they have in the middle of the ocean?

More traditional satellite networks, I guess? As I understand it, this is what sailors do / did before starlink.

This had me curious if I could find coverage maps of satellite operators, and I found this: https://www.satphonestore.com/coveragemaps

I'm speculating, but I'm fairly sure that they already have any and every satellite communication system available on-board, just as a back-up. If they're using Star link, it should be because it's working best.

Most sailors didn't (and don't) have reliable internet access.

I’ve absolutely no idea, but wouldn’t a satellite system higher up like Hughes have a better chance of working out there?