Delta extends a fee waiver - and they do call it a waiver on their website, so it clearly is an exception - to up to 8 companions travelling with a Medallion member. This exception is not extended to Flying Blue members or any other Skyteam Elite or Elite Plus status holders. (So, even if AFKL had a similar arrangement for their own Flying Blue elites, it would be very unlikely to extend to you anyway).

Airlines may differentiate with their own status customers, and some alliance members/partners may have some additional recognition for other partners' status fliers, but in general, when you are travelling outside of your home airline, you are largely reliant on the lowest-common-denominator alliance benefits. None of the alliances have a perk of extending baggage allowance to companions. In general, the only perk that can be "shared" tends to be lounge access, and that usually is restricted to one additional guest.