Since they can't do each property individually, they use comparable sales to make broad generalizations to determine percent changes.

Honestly, the people join our group if/when their #1 focus is raising more capital, so it's a pretty broad spectrum.

It's people like you who cause folks who would actually benefit from an ESA to be painted with the same broad scammer brush. 

What I'm hoping to find: I'm hoping to make connections, for mutual benefit; this could be investor friendly agents who have experience with identifying promising house hacks, investors who are looking for an additional financial partner, investors who are looking for a partner to help manage the load of projects (I am naturally drawn to planning and execution), and more broadly anyone who is willing to share experience and create new connections!

Now there is a whole array of ways this could be done, I'm not gonna run down that rabbit hold but fact is doing it all 100% on your capital alone is the hardest longest road.

., structural engineers, plumbers) for precision, or a general contractor for coordination if the scope is broad.

Even with 200 STRs it isn't a broad enough cross section to assume the changes.You would need to have millions of data points to show the trend IMHO. 

On another note; how do you get accurate data on flipping success rates when for a very vast array of them, it's not reported or substantiated anywhere?

With broad, high-level criteria, you may be able to easily cross of a number of neighborhoods where the numbers simply do not make sense (assuming you already have your buy box nailed down).

There are many I'm a part of like "STR Homes for Sale" and "Florida Off Market Real Estate" (I'm sure they have groups for different states) that offer a great array of off market and listed deals.