These surveys are always more about who answers than anything else - I suspect that one has a bias towards UK respondents. No way is Manchester worse than CDG or Berlin Schonfeld, especially the latter which is a disaster of a giant portakabin, still operating only due to the omnishambles of the Berlin Brandenberg build - and incidentally, any time anyone mentions German efficiency, mention that catastrophe to them.
But you can add any number of airports infinitely worse than Manchester could ever aspire to be, pretty much any of the Turkish regional ones, more or less any in India, or any in Myanmar (those are fun), or Indonesian regionals, etc etc etc.