The crowd on FT has traveled extensively enough to have a well formed opinion. It's not just sampling bias.
The issue is cultural. With many ME and Asian carriers employment is sought after and competitive. There is pride in the job. Not so much in the US so you get grumpy indifferent staff.
Flying the EU carriers in standard eco class shorthaul there's not much difference to flying in US in terms of the entire experience from departure to arrival. Flying in premium class longhaul I surmise there's more competition - from where I am OS LH LX can all be treated as "home" carriers in addition to other top carriers on other alliances .....whereas perhaps a US based flyer is slightly more captive to one of the big 3