These are the most consistently successful teams in the division. Not only that, but they boast the biggest stadiums, broadest fanbases and, as a result, the healthiest bank accounts. It’s been that way since Mansour took over City in 2008/9.
There’s plenty of articles in the web about the financial gap in revenues between the top 6 and the rest growing ever wider. Swiss Ramble is a great source. For those 6, with the right managers, they should blow the rest of the league away in a sort of mini league. And if you look at the tables over the last 10 years, by and large they have. Just the very occasional interruption by Everton, Leicester, etc.
What changed in 2019/20 is not that the league was getting harder for this bunch but Sp**s and Arsenal sacked two top managers and have struggled to replace them. Unai didn’t fall out of the top 6 but Arteta did twice. Any consistent rise of the middle teams to challenge the top 6 is a complete myth and put about as an excuse.
How is that relevant? City finished 10th in 08/09. By your logic there is a top 7 now with Newcastle's new ownership.
Can't find any articles talking about a top 6 prior to 2014. But knowing you, if they existed you would have provided them.