League finishes always gives a better view of reality. I reckon if you do the average position of the PL and Championship over the last 20 years there would be a group of 6 teams consolidated at the top comfortably above the rest but the same thing for the previous 20 years would have much more variation.
In the top 6 in last 20 seasons:
Manchester United, Chelsea, Arsenal,
Liverpool, Tottenham, Manchester City, Everton, Aston Villa, Leicester, Newcastle, Bolton, Blackburn, Southampton, West Ham.
14 unique teams
The 20 seasons before that:
Liverpool, Manchester United, Arsenal, Chelsea, Aston Villa, Leeds, Everton, Tottenham, Nottingham Forest, Blackburn, Newcastle, Ipswich,
Norwich, QPR, Southampton, West Ham,
Wimbledon, Sheffield Wednesday,
Manchester City, Crystal Palace, Derby,
Watford, Swansea, West Brom.
25 unique teams.
So you're right in as much as there was more variety, but most of those teams in the second list below Newcastle made only 1 or 2 appearances in the top 6 in 20 seasons.
It was still largely the usual suspects.