I haven’t really noticed much of a difference, though to be fair, I don’t travel anywhere near as often as many people on this forum, so my sample size probably doesn’t count for much.
Over the years flying with BA, I’ve consistently found Club Europe to offer a better overall service than Club World. Now that I know a BA cabin crew member and have some insight into their rosters, I can see why that might be. They genuinely look forward to some trips, dread others, and can’t wait to get certain ones over with… and while it’s not ideal, that does sometimes come through in the service.
Overall, I’d say it really comes down to luck of the draw… where your crew member is in their roster cycle, their ‘cabin roster,’ their personal preferences, and whether they’re heading to or from a destination they enjoy.