The biggest knock against Unsettled Mariner is the fact that it is likely difficult to find room for multiple copies, but the ability to protect your creatures (and yourself) from spells your opponents cast is potentially quite valuable
I think I can usually expect them to go heavy on removal, which helps with having time to cast it, so thats likely the card Id want more of to address this problem specifically
To start off we have a couple of sweepers with the Mythic Crackle with Power that gets better the longer the game goes and the spell exiling sweeper Draconic Intervention
The math on gambling for the specific card doesn't work Open 2-3 booster boxes at MSRP for bulk commons, uncommons, and most reverse holos, then buy the remaining singles
Or maybe they wont as the next big addition to the deck from Aetherdrift is Momentum Breaker, an alternative two-mana removal piece on an enchantment
The instant four cost is a Murder and they lose life too, and then suspends