It's true that pros discuss gear.
But (to generalise in a way that of course has exceptions) people who make money out of photography tend to use a top end UWA zoom, an f2.8 standard zoom, an f2.8 short telezoom, a large body that goes with this, and a bunch of super teles if they are sports togs or wildlife togs (though not many people manage to make a living out of the latter sadly). Then there are niches like architecture people that might have a TSE or two, and maybe a portrait lens or a macro lens for wedding, portrait and product work.
Who is asking for the fast primes? Me for one. But generally it's people who take pictures for fun. People who don't have to get any particular shot (note that that "have to" predisposes you to a large body with top of the line autofocus), but care a lot about the qualities of the pictures we do take. Also, those of us who take pics for fun try our hand at lots of things, so we end up with more lenses.
People making money from photography are likely to drive to their shoot (if it's not in a studio) and have all the gear in a large case. So once again size is not a huge impediment. People who do it for fun are more likely hiking, or travelling for another purpose with limited luggage, or just don't want something huge around their necks.
I'm not saying there are no professionals using Sony stuff other than the ones sponsored, but I'm sure there aren't many. I've never seen one in the wild.
Maybe there will be one day, but that day will be when mirrorless is mainstream and there are no advantages to SLRs. Sony would be mad to make the HUGE investment to try to get that market now in the last decade of mainstream SLRs, rather than positioning themselves for the future when the competition comes in a big way from Canikon.
Don't think though that I don't like the Sony stuff. I've switched to it. I've had more fun since I ditched Canon FF (keeping some lenses) and M43 than I've had with photography since my OM and wet darkroom days. I have loved the A7r and I'm waiting with bated breath for the A9. But the system really is optimal for people like me -- or like us, speaking presumptuously for many people on this forum. People who enjoy legacy lenses, people who agonise about Bokeh, people who are about levels of IQ that aren't commercially significant. People who like to feel ahead of the wave (which is something that is commercially unwise)
Sony has indeed talked about getting a pro camera -- and they have started having pro service programs. But what "pro" means here is just very good (as in software names: Doitall Pro 2.0!). Incrementally better and non-incrementally more expensive. Will some pros buy it and sign up for the pro service programs? Sure. Will they in the long term get a big chuck of the professional market? Who knows. But will pros be the life blood, or even a decent chuck of the market for the A9? I doubt it. It'll people like me - us.