Britons elect MPs. Europeans elect MEPs
Britons don’t elect the prime Minister, Europeans don’t elect the commissioner.
Britons don’t elect Whitehall. Europeans don’t elect Brussels.
I suppose you could argue that “first past the post” represents some vital democratic principle, but it would be a weird argument.
Any attempt to make the European Commission more democratic would likely be met with howls of protest that this would infringe on sovereignty or whatnot.
