Premier League is all about Big Four

In recent years, the Premier Leauge has been claimed to be the strongest league in the world. I doubt that. It's all about the big four. I don't think the strength of four teams can represent the strength of the whole league. The semi-finals of the Champions Leauge has been dominated by the big four for a few years, but, to me, this just shows that the big four has been the topest five teams in Europe or, maybe, in the world. Once I had been convinced that the Premier League was the strongest league. However, since yesterday I have had doubt. If the Premier League is the strongest league, how come there is no english team in the semi-finals in the UEFA Cup? Although what I call mid-tier teams (I don't know if there is the term.) seem to be stronger (like Everton for a few years and Aston Villa for this year), they are just getting stronger in their own league rather than in the european games. It may be reasonable to say the rate of getting stronger of the Premier Leauge is greater than that of other leagues. In my opinion, there has to be more teams in the final stages of various rather than one international club game if a league is to claim to be the strongest.