Interesting stuff, Moxie. I don't fully agree, though, abut what you say in the second half. I think this is
partially true, but also that there was a legitimately weak generation of players born from 1989ish to the mid-90s. Talent does ebb and flow, with different cohorts of talent coming up, some stronger than others. So in that sense, yes, the Big Four has suppressed the younger generation, and I think there's something to homogenized courts, but it is a combination of great older talent and a weak younger generation, otherwise this would show up in more minor titles won by young players. The Big Four dominate the big tournaments, but they don't play in many of the ATP 500s or most of the ATP 250s.
We can also see this in the number of young players in the top 100, compared to past eras. I actually have a chart to share.
Before you think, "Dude, WTF?" Let me explain. I was working on a research project about young players. The above chart is an abbreviated version of another chart that has the names of the ten highest ranked teenagers in year-end rankings from 1985 to the present. There are different shades of green corresponding to different ages (17, 18, etc); the darker, the younger. The very light green are 19-year olds, the middle green is 18, the darker green is 17, and you'll even see a few players that are very dark green 16-year olds (e.g. Rafa and Gasquet in 2002), and one almost black-green 15 year old (Chang in 1987).
Anyhow, as you can see, the top ten teenagers really start dipping after 2005, which was the last year Rafa was a teenager. By the time you get to 2009 there are no teenagers in the top 100 - compare that to 1989, when there were ten in the top 100!
This "dark age" of young talent really lasts from 2009 to 2013, which are the years that players born from 1990 to '94 are 19-years old, or 1991-95 are 18. The only two teenagers to end the year in the top 10 are Bernard Tomic and Ryan Harrison in 2011 (a 19-year old Grigor Dimitrov finished 2010 at #106).
But things start improving in 2014, when you have Nick Kyrgios leading the pack at #52, 18-year old Borna Coric at #102, and a 17-year old Alex Zverev at #136. And you can see incremental improvement in 2015 and 2016.
So my point, again, is that while I think what you say is true, it is only partially true. The Big Four are great and did suppress young talent, but the young talent born in 1989-94ish was particularly weak, otherwise there would have been more teenagers higher in the rankings and winning minor tournaments.