I’d have to say I’ve never experienced this, including at the LH lounge in LHR and elsewhere in their wider network. Nor do I ever recall being looked down on for being at BD Gold, which was regarded as the most generous FFP in the Alliance for many years.

I would be astonished if many lounge agents actually even knew what the qualification requirements were for the various schemes. Any perceived slight seems much more likely to be in the mind than nested in reality.