Deadpool should generate more interest than the last few MCU movies. We get to see Jackman/Wolverine that is a boost similar to Sony having the previous Parker's. He is going to joke on the current state of the MCU or that they need him. I really liked Deadpool 1 but the 2nd one was just okay, it had some moments. This I am hoping goes up to 1 level.
As for Deadpool saving the MCU, it will take more than 1 film to save the Mcu. They need to cancel/trim down their annual originals coming straight to Disney+. When it comes to future movies, the success of Deadpool wouldn't guarantee that Captain America, Fantastic 4, Thunderbolts and Blade wouldn't flop in 2025. Those need to be good, marketed well and released at the right time. Dumping them all in 2025, is not wise imo. Who knows if Avengers 5 and 6 aren't critical failure, etc.
Unless the trailers look bad, which I doubt, Deadpool 3 will be one of MCU's highest grossing movies.
But. I don't think the MCU will return to the glory days ever again. It's gonna have its big movies here and there, sure, but the days of each installment being "we gotta go see the next one!" are gone. Superhero fatigue is real.