Good question. I have asked myself the same, but I have never had to approve a voyage on any of these vessels, so it has never been an issue for me personally.
I did have the same problem taking command of a Drillship with wheelhouse aft and not much visibility dead ahead. The arrangement was approved by flag state and class though.
My solution was to place a lookout on either bridge wing, day and night, 24/7 while under way.
There were a CCTV in the derrick that could be used to look ahead, but as far as I’m concerned that is not an acceptable and legal solution, no matter how much the Toolpusher insisted that he needed the crews to work for him. No other Captain have ever insisted on this, apparently.
A few months later, the ship had a minor collision in the Singapore Strait and got a lot of the blame for that particular reason. No proper lookout and no clear visibility ahead.
Most other HLVs with aft superstructure and bridge have a fwrd. bridge, which is accessible via a tunnel from fore to aft as seen here: