I think you are all missing the real reason for multi-branded dealerships. It has nothing to do with the specific tech or specialist. It has to do with sound business and market share and money. Listen, as an example, Dealer A sells a green truck (the mfg is not important) they have done a good job and are now scrambling for ways to grow their business because they have either saturated the market or they have just run out of new businesses and the new businesses are so few that the competition is incredible.
Now, there is an opportunity to buy the local yellow machine. Almost automatically the original company increases their business and their foot print in the market. To your point about tech's ideally it would be a perfect world to send the yellow truck specialist to work on the yellow truck and the green tech to work on the green truck. But we aren't in a perfect world and to be honest, more times than not dispatching from various locations actually saves the customer and the dealership. Multi-line dealers have been around for years. Some are very successful and are able to sell all the lines that they represent, some are happy to maintain their primary line and supplement additional sales with the other lines.