A 'Big 7' has formed in men's tennis over the past 2 years

Just the title. If we look at the 2 years span starting at the 2018 ATP Finals stretching to now, it's very clear that there are 7 elite players who going into any given match against someone outside the group will be strong favourites, who will expect to make deep runs at any given big tournament, and who generally stand far ahead of anyone ranked 8th or lower. These 7 players are of course Djokovic, Nadal, Thiem, Federer, Medvedev, Zverev, and Tsitsipas.

Over this period, I count 21 'big' tournaments as having taken place - 7 slams, 2 tour finals, and 12 masters.

Of those 21 tournaments, 20 have been won by someone in this group. 15 of these finals have been contested by 2 members of this group, including all 7 of the slam finals during this period. No one outside this group has reached more than 1 final of a big tournament.

The figures are as follows:

Djokovic - 10 finals, 7 titles

Nadal - 6 finals, 5 titles

Federer - 3 finals, 1 title

Thiem - 5 finals, 2 titles

Zverev - 4 finals, 1 title

Medvedev - 5 finals, 3 titles

Tsitsipas - 2 finals, 1 title

***

Fognini - 1 final, 1 title (current rank 17)

Lajovic - 1 final, 0 titles (current rank 26)

Goffin - 1 final, 0 titles (current rank 15)

Schwartzman - 1 final, 0 titles (current rank 9)

Raonic - 1 final, 0 titles (current rank 14)

Isner - 1 final, 0 titles (current rank 25)

Shapovalov - 1 final, 0 titles (current rank 12)

I imagine looking at rankings, head to head records, semis etc would add to this picture. It's not just the success of these 7, but the lack of consistency of those trailing them.