If you want miles towards EXP, you don't have to stay on AA code-shares. You just have to stay within oneWorld*. In a few cases deep-discount partner fares don't earn full (or any) AA EQMs/EQPs, but your choice within oneWorld is still broader than just AA and its code-shares.

You'll find lots of useful posts on oneWorld RTWs in the oneWorld forum. Much of that forum is devoted to one sort of RTW fare or another, with ideas on how to maximize miles within a fare's rules.

A problem with some RTW fares is a minimum duration of ten days. This is to keep people from doing exactly what you want to do: saving money on a short business trip. The above post by tt7 is one way around that rule.

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*And AS, but AFAIK you can't use their flights on OW RTWs.