There are two good reasons why the AF/BE arrangement is a bad thing:
1. It's basically a cartel rather than competition ie there is no competition on the MAN-CDG route. That's why fares are high.
2. It's mis-selling ie paying for a higher quality product and receiving an inferior one instead. You pay for an Air France Business Class ticket from MAN - CDG - XXX and you will only get business class on the CDG-XXX portion of the flight if you are unlucky enough to be on an AF code share operated by BE.
This happened to me once last year on a returning trip when after a long 11 hour AF flight, I ended up completing my journey on a crop duster surrounded by the cliche Disney family complete with screaming brats kicking you in the back. Yet my boarding pass still (rather pathetically) said 'Business Class' in big letters across the top. Personally I think that's fraud.
Result: AF now are on my 'avoid list'. KL will go the same way if they out-source their flying to BE.