Believe me, I'm even more worried than you. I think Melanchon would actually do more damage, as crazy as it seems, Le Pen is incompetent and a sellout, Melanchon actually believes the BS he vomits.
Macron finished the traditionnal left and right wing parties, which were too large and rotten to the core, but it's left us with a large center and two extremes, it's high time we have the normies left and right come back.
If the extremes are unelectable, the center party should split eventually. They'll find something to disagree about.
As long as they are more terrified of losing to the extremists they'll try to keep it together as long as they can. I hope they don't become too corrupt in the process.