*A is far better than the alternatives OW and Skyteam.

United and LH always 'competed' on the same routes altough they have revenue sharing. Try AA/BA and you will know the difference: no miles on all cheap fares, no miles on AA flight number with BAEC etc etc.

SQ always refused miles when any segment of the trip is on a certain fareclass.

Double or triple lounges in a certain location have evolved out of history or terminal locations.
Different checkins/ground handling have to do with level of service. Some airlines would like to offer a better deal for their customers. Just imagine if all intercont handling of*A was done by UA and everyone would have to head to an RCC

These does not necessarily indicate a weakness of an alliance

Memberships in the alliance are linked to ownership: KF,JK,BD,LX,OS

FFPs differ to offer the best for their markets. Some are restricted by local laws. LH in germany, SK in scandic, etc.