I very much agree that a decline in MFL is a bad thing.
I don’t agree actually that it is so very much harder for native speakers to gain a high grade. If the A-star GB is 360/400, and a non-native gains (say) 380/400 (perfectly possible; it's not a competition and native speaker fluency is specifically flagged as not being needed in the speaking assessment, for example) then they will get an A-star. No matter how many native speakers also get a top mark.
It’s not an easy choice tho for A level, I do agree. A B at MFL A level is a hard-won grade. And a native speaker is not guaranteed a top grade. Someone I worked with last year gained an A even though they were basically a mother-tongue speaker – they worked really hard but there were other reasons why they didn't quite get an A star. It’s not a given. Nor should it be obvs.
I do think the A level spec is good tho. It’s current, engaging, deals with real-world issues (immigration, the changing family, francophone music and cinema, the reunification of Germany) and it really is challenging. I think it's challenging for a native speaker as well, as indeed it needs to be. Hard work? bring it on.
I do see the point about maths (and I think it's fair that a lot of maths A level takers are more able mathematicians); maybe for a less-able student essay subjects are a better idea as they are more approachable for all. Interesting discussion!