Shinano as a repair ship still depends on the wider force

Would Shinano have made a good aircraft repair ship?

Yes in a stronger and earlier Japanese force structure, but late in the war there was too little viable carrier aviation for the role to matter greatly.

The question returns to the central point that support ships gain value from the combat system around them. Shinano could repair aircraft and help sustain carrier aviation if she entered service while Japan still possessed aircraft, trained crews, and operational carriers. A 1943 arrival in a delayed-war scenario would therefore make the role much more attractive. Arriving historically late, after those surrounding capabilities had collapsed, sharply limits what even a completed repair ship could accomplish.