Luck can be a factor in a one-off cup run, but it’s pretty irrelevant in multiple wins in the same era. Liverpool were not lucky cup specialists, they fully dominated the English game by winning 7 league titles in 9 years. And it was clearly a strong league given the competition of Nottingham Forest and the simple fact that English sides won the European Cup six years in a row. Ultimately Liverpool were unquestionably the best team of their era because they consistently beat these 'better teams' and have the domestic and continental trophy haul to back it up.