This in a 1960's DC-8 at high altitude.
Yes, but surprisingly those wings were thinner, less super-critical, more sweep and could well have had higher Mcrit, surprisingly - just less optimised for the 'exact' cruise condition and fuel volume/sweep trade-offs..
I doubt you'd get an A330 above M 1.0 (in one piece)
Also, the lower by-pass, or even pure jets of that day, had much less momentum drag and indeed, the naceles also likely again, a higher Mcrit
Ditto fuselage diameter
But I'm not arguing your general case-making and assertions...