1, 90-00 Arsenal, Leeds, United, Blackburn.
00-10 United, Arsenal, Chelsea. Post Roman in this decade only United could compete with Chelsea.
10-20 United, City, Chelsea, Leicester and Liverpool. Bar Leicester which was a fluke and probably won't happen again only United at the start of the decade and Liverpool right at the end stopped City and Chelsea dominating.
Let's see how the next decade goes. Especially if the Saudis buy a team.
2, Blackburn spent no where near the type of money City and Chelsea do. A local businessman done good invested a 20-30 million and his hometown club were able to win the PL. That won't happen again with nation States Bank rolling teams.
3, That's largely to do with the CL. Germany has always been dominated by Bayern to some extent. Same with Barca and Real in Spain. Before Juve Inter won 5 in a row. France is being dominated because of a gulf state buy out.
Arsenal, Blackburn and Newcastle were able to compete fine without billionaire owners in the 90's before Roman came along.
Yes FFP was a joke and City and PSG treated it as such. They'd do the same with a salary cap enforced by UEFA. That's partly why 10 of the clubs wanted a super league with strict financial limits that teams had to agree to
I think you're not taking into consideration the kind of inflation that went on in the late 90's and early 00's which meant Chelsea had to go much higher.
Firstly, when Blackburn won the league the world record fee was £13m and when Newcastle tried, they actually broke the world record fee at £15m.
By the time Chelsea cam along the world record fee was £45.5m, so three times as much as Newcastle and Blackburn. As another poster pointed out, Blackburn also went 3x more than Utd to get close to them in 95, looking at gross figures is really a bit misleading as it doesn't consider the wider football market.
Then, as you point out, if we're looking at decades of different winners things are improving. We can try and predict all we want, but we do not actually know City will win multiple titles in a row. Hence, we have to accept things have improved in regards to competitiveness and this is not replicated in the other big 3 leagues:
Germany
1990-00 - Kaiserslautern, Bermen, Dortmund, Stuttgart, Bayern
00-10 - Dortmund, Stuttgart, Bermen, Wolfsburg, Bayern
10-20 - Dortmund, Bayern
Italy
1990-00 - Sampdoria, Milan, Juventus, Lazio
00-10 - Roma, Milan, Juventus, Inter
10-20 - Milan, Juventus
Spain
1990-00 - Barca, Real, Atleti, Deportivo
00-10 - Madrid, Barca, Valencia
10-20 - Madrid, Barca, Atleti
The PL, is the only league where the competitiveness has improved. Furthermore, in Germany and Italy not only have they gone from 4-5 teams winning in a decade but of the two they have winning in the 10-20 decade the split is 2 v 8 and 1 v 9 respectively.