Think what you want, but bottom line is AA standalone (also AA/US combined) are and have historically been much larger/stronger in STL than MCI. MCI has very limited mainline service, STL is seeing increased large RJ service which shouldn't come as a surprise to anyone.

Lets see STL has:
-Service to all hubs (plus PIT as point to point/legacy hub)
-Flight Attendant Base
-Modern new Admirals Club
-Line Maintenance
-In-house TWU fleet service
-Easy single entry for security with TSA-Precheck.

MCI has none of that. I don't even think MCI has catering capabilities, at least for AA. AA has many more local based employees in STL (all that's left at MCI is above the wing agents), more facilities, and more operations. They do however, have below the wing staffed for US Airways with IAM represented personnel, however it is among the smallest if not the smallest single US station with in-house fleet service. US contracted out STL in their second bankruptcy and used third parties until earlier this year when AA TWU took over that handling (as US IAM has also done in a number of locations)

MIA-MCI hasn't performed well, they continue to draw capacity from the market. If MIA-MCI was such a great market to serve they wouldn't have waited until 2015 to add it, would have come online back in the 2007-08 timeframe.

I've moved on from STL, been gone since 2008 and am not here to beat the drum and reimesce of the old days. But to say AAs operations and presence there will look like MCI is foolish, IMO.