Yeah, was gonna say this. The money in England means that the salient point here is less about Leicester competing with other English teams. It's more about the ways English teams can compete with the rest of Europe. Leicester could scout the entire world and give players a) competitive wages and b) an incredible platform.
The budgetary margins from Man Utd/City to the others might be vast, but the reality is, as you've said, that there's a law of diminishing returns whether you're paying 30m or 80m for a player.
Most Scottish top flight teams would struggle to match English Championship wages, possibly League One. It's a real shame the wage cap has been scrapped as it could have played a huge part in raising the quality of players that clubs like yours and mine could have attracted.