Ok so I just came back from a blackwater trip where I was using the 90mm macro on Sony A7C... it was an uphill battle for sure.
I came back and have been asking around on what the best options would be for BW on Sony FF... the 50mm macro unanimously got a "it's horrible / it's even slower than 90" from everyone I've spoken to. My buddy was shooting Sony A6600 w canon 60+metabones and I tried the combo on land (but did not get to borrow it on a BW dive as we both did every dive) - it did not feel notably faster than the 90 to me and is still prone to hunting. It also vignettes a bit around the corners but I suppose for BW that doesn't really matter. Someone else told me they shoot A1 with the Nikon 60+monster adapter and it focuses well and is easier to use than the 90, but as it's on A1 I'm not sure how an older body will handle it. Both Canon 60 and Nikon 60 + adapter options work with the same port as the 90mm (for Nauticam).
And then lastly my Nauticam dealer who shoots A7IV told me the 90 is much faster with EMWL and he uses it with 100 degree objective for BW, as does 2 of his other customers one of whom shoots A7R5 and the other A1. He said out of all the combos that gets him the best results for BW, but I've haven't really seen that combo advised elsewhere.