The French Open doesn't matter for Roger Federer.
In fact, no more tournaments matter for Federer.
At this stage of his career, he has already cemented himself as the greatest player of his generation and one of the greatest Wimbledon players of all time. Furthermore, Federer has become one of the first names mentioned when discussing the greatest players of the Open era.
This French Open is so small in the grand scheme of his career. Sure, winning some more Grand Slam titles would be great for his resume, but they aren't necessary. He already has the most singles titles in the Open era.
Federer has won them all. Wimbledon was his court (six titles), and he made the most of the U.S. Open as well. When you add them all up, Federer has an astonishing 16 Grand Slam singles titles to his name.
You can credit weak competition all you want, but Federer was in a class by himself for nearly an entire decade. He deserves credit for his greatness.
Additionally, the French Open itself is practically meaningless to Federer. He isn't spectacular on clay, and he has struggled to win in the past. However, in 2009, he expelled those demons and won the tournament to complete his career Grand Slam. Unfortunately, the win didn't come against Rafael Nadal, but it was sweet enough.
Federer has nothing left to prove. He's won every major tournament. What's more, he's spent the second-most number of weeks at No. 1 in the world (one short of Pete Sampras), and has the record for the most consecutive weeks in the top spot at 237.
For over four years, Federer was the best player in the world. No one is even close to that mark because that's how great Federer was.
Sure, this win would be great for him. Every professional athlete wants to win a big tournament, regardless of age or form. However, this has no negative impact on Federer's legacy.
Federer is cemented in the tennis history books. He's done it all. He doesn't have to do it again.
He's the greatest player of his era. He has nothing left to prove.