All a bit different for me, as I grew up in Sweden where we certainly did not have the option of dropping subjects we didn't like (not even foreign languages). And I believe the French bacchalaureat is similar.
The idea behind it is that people who have a vote need a certain basic understanding of how society works. We live in a democracy and that means civic responsibilities.
Still, at this stage, and looking at your ds's particular situation, there is the risk of a last-ditch attempt to catch up now taking time from subjects he has a better chance with. So it might be worth just cutting his losses.
On the other hand, you have to understand that the school can't suddenly provide a new teacher to take extra classes, particularly not for a teenager who has sat on this problem for 2 years without taking any responsibility for it. There just isn't that amount of extra money going around.
I would sit down with your ds and discuss the whole thing with him in a very matter-of-fact way. Explain how various choices (trying to catch up, cutting your losses etc) may affect his future career prospects.
Also, make sure you mention that in any job he chooses, there will be times when his boss tells him to do something he finds difficult and pointless, and that if he doesn't do it to the best of his ability he will find himself out of a job. This is grown-up life. But mention this once- don't go on and on about it.