When an EXP topic arises, as a mere PLT I adhere to the maxim that "children should be seen and not heard," thus I never weigh-in.
Until now, that is.
I believe what happens with a split vs. not splitting is the following: If not split, you and your companion receive the upgrade at the same time. Perhaps however not as quick as you are accustomed and only after the AA, algorithmic process determines that other status members will not be disadvantaged because of your non-status companion receiving an upgrade.
In those instances in which an upgrade goes through for both you and your companion at the same time, let’s say the 100 hour mark, the AA algorithm has estimated that potential revenue tickets as well as other EXP, PLT and GLD upgrade requests will be met based on the available inventory. As a result, you are simultaneously upgraded to F cabin.
If you split, you get the benefit of your EXP status and an early upgrade to first. Your traveling companion must wait if the above conditions have not yet been met.
I think I got that right.