Diamond in the UK for the last 10 years. Majority of travel in Europe. My experience has generally been good. Always get an upgrade, loungwe offerings mostly good. Only time I saw a seriously overcrowded lounge was Munich last December when there were a significant number of US visitors.
So for me, I haven't seen any reason to change.
Perhaps Hilton needs a just US diamond version and to leave what they do with Europe we'll alone.