Sinclair is a horrid company, 100% anti-consumer, but in no way is it "responsible" for the changes to the regional sports system. Really no one is, it is just a function of technology.
The old system. "Everyone" had cable/DBS and this included the local RSN. The local RSN is a unique thing, very expensive and in many markets the most watched single channel during baseball season, but in a 100 to 200 to 300 channel world, most watched still means only a small %age of the total. But everyone paid, and paid a lot for it. Then there was MLBEI, which is just the games on other place's RSNs (which would not exist in the first place if the RSN for that place didn't) which was only available as an add on in cable/DBS, for people who had already paid for their local team.
The new system. Some people are out to save as many cents as possible and do without linear TV altogether, but more than that many are switching to alternative internet based linear providers. Most all of which do not have the local RSN. Those that care about their local team, of course, stick with DirecTV or DirecTV stream, or their local cable provider, but, again, that is still a small %age of the total. And MLB now offers mlb.tv and again a smaller version of it as a part of ESPN+, as Disney desperately tries anything to save its money gushing streaming venture, without first paying for local baseball.
None of that is Sinclair's fault. All you can really fault it for is getting out-smarted by a combination of Disney and Fox in buying the asset just before this seed change became apparent.
The problem is not going to get better. Without the RSNs there is no mlb.tv to sell in the first place, and mlb.tv is so cheap because it is just gravy money, selling Royals games in Maine to what few might want them for pure profit, the big money having already been paid by the folks back in Kansas City and environs. RSNs are something like 33% of team revenue, and, really New York is a "large market" and Cincinnati a "small market" BECAUSE of the different number of RSNs viewers. Live gate has nothing to do with it. I could draw the same 45K a game in Omaha or Boise or Birmingham. And selling the RSNs "a la carte" is probably the dumbest move they could make, why any cable company would continue to carry a channel, at a high price, in fact almost the highest price of any channel, that 95% have no interest in, when they could just tell their customers that want to it buy it as an "internet add on". Congratulations, you just got $15 or 20/month from 5% of the population, rather than $8 from what was 90% and is still in the 60s. Genius.
There are solutions. Which involve putting the genie back in the bottle vis the ability to buy other people's games without first paying your fair share for the local team, but customers will howl about that. Too bad. Still the problem is that most people want NEITHER their local team, NOR anyone else's either. That is not going to change.
BTW, flash forward about 5 years and substitute "ESPN and FS1" for "RSN" and the situation will be about the same.