I think what he's saying is that if they ever decided to go professional, choosing Nikon/Canon would make for a much easier and reliable ride.
I do know professionals who shoot Sony, but most are natural light family/senior portrait shooters who don't need rentals or lots of compatibility and support in the first place.
In all honesty, Nikon uses Sony sensors and they have a wider range of lenses and features, so I'm not exactly sure what the benefit of having a Sony camera would be unless you were going to buy the A7/R/S full frame mirrorless.
EVF, high FPS, Better AF-C in certain cases...
Meh, the EVF is a personal choice. Often times when I'm using my X100S with flash I have to turn it to the OVF because the screen is too dark (Sony cameras probably have a way to turn off exposure simulation though do this point might be moot). And those other two points are advantages of the SLT at the cost of low light performance due to light lost with the translucent mirror.
Add to that Sony's lack of support, lack of lenses, and lack of dedication to one system; it really puts a damper on my enthusiasm for Sony cameras.
I think that he EVF is about the only real advantage I could see since they're actually becoming quite useable, otherwise, there are just so many drawbacks (in my opinion) for going all in with Sony SLTs/DSLRs