The "dark and gritty superhero" formula is not sustainable

You're not wrong. There needs to be a balance or at least more variety. People are through with the DC's doom and gloom schtick and grumbling is arising over the MCU formula. I think the first superhero movie boom in the 2000s for all the faults in their output, had greater variety in superhero/comic book films. We had bright and colorful with Sam Raimi's Spider-Man, dark and gritty with Daredevil and Hulk, the middle-ground with X-Men, strange and quirky with Hellboy, mature and adult with Batman Begins, kid-friendly with Fantastic Four, and just plain silly with Catwoman.