Whilst i think it is getting large, for the better for us perhaps as we have more carriers we can choose to clock our miles to, but there are some benefits from size for star -

* *a transit buses - you don't need to operate seperate buses for each carrier, such as the *A bus in LAX, NRT, etc. The more carriers, the easier it is.

I'm sure there are other handling, sharing engineering, checkins, loading pax on other *A carriers for missed flights, etc benefits

I noticed OW said it's membership for new airlines was closed until further notice and they were trying to consolidate and improve on the alliance airlines they currently have...