Correct 100% miles on all booking classes, and that's determined by the operating carrier, not by the ticketing or marketing carrier. So if you have a flight on United no matter how booked, it's 100% credit for Economy.

And yeah I know it's strange, but the codeshare cuts both ways. Sometimes it costs more, sometimes less. The airline world is a strange place I'll often look for both codeshares and with the operating airline when booking.

The price you pay is determined by the fare published between origin and destination by a given carrier. These fares often allow travel on partner airlines. However, it's the fare that determines the cost, not the choice of partners. If AC is trying to undercut LH they'll lower the cost of their fare, even though that basis may well allow for travel on either carrier.