I think because we have won six already and there are a sprinkling of other replicas with our PL compatriots, I would cherish an undefeated league above a trophy. I know it's trophies that count, but trophies are a symbol of achievement. Undefeated over 38 games is an enormous achievement. Its far easier to name the only undefeated PL team than it is to name the winners of the European cup, simply because to-date it's a unique achievement. Winning a CL double would be magnificent a double, again because of scarceness. But I don't think should be so much ridicule for the original question.
We mocked Pep last season for saying the league is harder to win, but in most seasons the team that the won the PL is better than the one that one the cup. There is some weird thing about some teams being better at cup competitions too. But in the whole the league is the metric of the best team in the land ( quite often league winners go deep in the domestic cups, backing this up).
Luckily there's no rule to stop a team going unbeaten and win the cups.
--obviuosly unbeaten and not winning the league is meaningless, but doubt we are ever seeing that.