I can totally agree that it's become a bit over romanticized as a backlash to how underrated it was when it came out, and I think it's a great record, one of my favorites, but I can admit it's not the absolute life changing work of brilliant perfection that we sometimes make it out to be.
For the sake of discussion though, I will say that for a lot of Green Day's older fan base, people who got into them in the 90s, I think Warning kind of represents this last graceful hurrah during a time period where they were fading from relevance and popularity, which was a bittersweet and kind of sad moment to witness for a lot of us back then. Those who were there remember really supporting the band when they had really fell from the top, despite putting out great work, which is hard for any fan to watch. Warning captured that bittersweetness really perfectly for me, and on top of all of that, the album came during a time when myself and a lot of their fans who had grew up with the band since Dookie, were coming of age themselves... graduating high school, maybe saying goodbye to friends and moving on to college, or starting to join the work force for the first time... I think it kind of weirdly hit all the right feels for a lot of us in 2000, both where the band was at, and where we were at ourselves.
I love how Warning captures a moment in their career, as well as a moment in their fans coming of age, both which have become tied together in a tangle of bittersweetness, that the songs on that album really highlight. The fans who were there and experienced what I'm referring to, probably have a similar attachment to Warning, and as such probably praise it to the rooftops, despite the truth being, that it's just a solid pop rock album, not the savior of mankind that we sometimes refer to it as. But isn't that the magic of music? Sometimes even just the simplest rock record can mean the world to someone, given the right context.