1. Stars were coming to the PL well before Abrahimovic e.g. Cantona, veron, Ginola, Zola etc
2. He didnt bring about the big 4 era. It was Mourinho that brought about the big 3 era. Liverpool were rarely credible title challenger back then and even now. The big 4 era started when Man city became a title contender and won their first championship.
3. PL started its popularity domination in the 1990s as they were the first league to truly commercialize the game both at the league level with TV rights and at the club level with United being the leading example
4. He was probably the richest man to take over a premier league club wen he did, but he wasnt the first rich owner in europe. If any at all, Berlusconi was the archetype football godfather+sugar daddy wielding both his financial and political influence to the benefit of the Rossoneri. The FFP and similar changes to the qualifications and revenue distribution of the CL are a reflection of UEFA succumbing to the pressure from the G14 clubs who would like to keep all the money for themselves. It has been an ongoing battle since the 1990s (as football became more profitable) but I agree that the potential threat of sugar daddy clubs added to it.
Roman's acquisition of Chelsea has influenced the evolution of the premier league, but so did the downfall of leeds. I wouldnt go as far as to call it a watershed moment.