People having even less incentive to donate to the Mines on the Island,
Your criticism makes sense if you have only one town on an island, but if you have more than one then it makes less sense. Remember that you not only have to level up the Employment Bureau but also the Town Hall and other buildings. At some point there's a tipping point; an inflection point. Just like with the other improvers.
I'd also disagree that it is self-balancing just because it needs Population,
Have you considered the cost of high level Town Halls? Then there are the high level Museums and Taverns to keep the population happy. And high level Temples to keep the Faith high. And high level Hideouts to protect the town. It's very much self-balancing.
Also the building would make Helping Hands pretty useless,
I disagree: you can use Helping Hands on top of this, and without the building too.