I like the constructor implementation early game.
However I do agree that their purpose and utility drops by the time you get to mid game and they just end up being parked somewhere or disbanded. Except for mega projects ofc.
Science ships at least get the 'assist research' option. I would like to see constructors get a similar function. That you can 'assist construction' on a planet and get a build speed bonus or something.
To limit spam it would make sense to have an engineer leader.
I would take it further and say we shouldn't have governors at all. Rather, you should appoint a scientist, engineer, admiral, or general to govern a sector, or become your ruler, and this choice would result in appropriate sector buffs or debuffs.