I think the blend is both for speed and flavor. The meso bacteria typically acidify faster at the initial temps, because you make mozz at around 90 and then bring it up to 105. But even fresh cheeses taste and smell different if made with thermo vs meso, so adding some thermo to mozz helps to give it a more classic flavor, while still having fast acidification.
I've never made a provolone with meso culture, so I can't say what the exact difference would be, but it would be a different cheese than a classic aged provolone. Thermo culture usually has rod-shaped bacteria (bacilli), whereas meso culture usually has ball-shaped bacteria (cocci). They are very different, even to the point of producing different isomers of lactic acid (+ or -, this influences fresh mozz flavor), and release different enzymes from their cell walls and bodies contributing to aged cheese flavor.