The flaw I see in the argument is that yes companies who treat their employees well will see better outcomes; however, we are not talking about the labour pool of a company (which is limitless), we are talking about raising the wage floor for the entire labour market which is a zero-sum game.

In my opinion raising the wage floor for the entire labour market will not then have the same positive impact for companies in general as those measurable for individual companies who already pay good wages.