IIRC, except for AC in T2A, most of the *A airlines have been at T1 for several years.

I think one advantage for AC flyers arriving at T2A has been the ease of onward cnx to AF's network to points in France, Africa and elsewhere not served by AC or *A from Canada or over LHR, FRA, BRU, etc.

The easy walk from T2A to T2E/2F or to the SNCF TGV station was also positive in IMO.

Perhaps AC mainline service to places like LYS and NCE currently and next year TLS and BOD reduces the interest of being so close to AF ?

Not sure any versions of the CDG MLL (or previous ADP contract lounges at T2A used by AC) were great places to spend alot of pre-departure time. Nor were any of the lounges in T1 (circa 2002-2006), like the dire BD Diamond Club lounge in one of the satellite basements or the Blériot and Éole lounges up on the 10th floor of the round main terminal.

One positive point at T1 was the ease of access to the rental car counters on the upper floor parking levels via elevators from arrivals.

I have not been to T1 in years and will be looking forward to checking the place out again in 2023.

Way back in the olden days at T1, you could easily see and talk with the unfortunate man who was the subject of the Tom Hanks movie "The Terminal" (filmed at YMX !)