Feel free to criticize them or not, their success doesn't matter what you think about them. They got to where they are by fondly remembering a time in the 70's, where Jimmy page and Robert Plant were Gods to young men. But they got to the point that they are at, and got no further. They will never be even remotely close to as popular and cool and succesful and LZ once was. The thing is, that music just isn't cool anymore. Take a look at jimmy page–he's not on stage in his dragon outfit, dick outlined by his leather pants, high on heroin, with a cigarette in his fret hand doing insane solos for some crying girls in the front row. Nah, he's just about completed his transition into an elderly chinese woman. He's your cool grandpa. He's not doing drugs and taking home a nice young lady after each concert. That dude today is the Weeknd, or Drake, or Shawn Mendez.
To be cool in music, you have to be pushing the boundaries of your genre. Looking good isn't good enough to be a huge success. You have to give the world something they've never heard before. People are quick to say LZ ripped off earlier blues artists like Muddy Waters or Robert Johnson. But did they really? Why is it that LZ was wildly more successful than either of those guys, who the average dude has probably never even heard of? Is Jimi Hendrix's "All Along the Watchtower" a rip off of Dylan's version, or is it its own masterpiece? What about variations of "House of the Rising Sun" by The Animals or Frijid Pink? They're all rip-offs.
When it comes to art, you don't have to reinvent the wheel every time. You simply cannot erase your memory, forget any influences, and start fresh with a tape recorder and a keyboard. If that were the case music would never evolve over time, it'd just be the same simple shit over and over again. The blues, like any genre of music–country, folk, classical, etc.–started from total authenticity. Just a pure expression of emotion, with little technicality. You ever watch a video on youtube of some African-American blues guitarist from the 30's playing his guitar down by the river, he'll be playing on a half-decomposed acoustic with only one string, but it sounds like the most genuine music you've ever heard. He could just as well been playing on a rake and it'd sound more real than 99% of the shit on the radio today. It was not for the purpose of looking cool or selling records. But it can't stay this way forever in the face of a capitalist economy. And popularization of music isn't always for the better or for the worse (as in today's popular music).Every time a new artist takes over popular music (like Queen, The Beatles, Michael Jackson, Led Zeppelin), it's because they brought something new to the scene, and made it appealing to the masses. Jimmy page grew up listening to early Blues artists and was heavily influenced by them. He took elements from that, and completely reinvented it with his solid body Telecaster and Les Paul, Marshall amp and tone-bender fuzz pedal. And he, and Led Zeppelin, gave the world something they had never heard before. It was Blues, but overflowing with youthful, and sexual energy. Led Zeppelin made the Blues marketable to the masses; to the young, white, heterosexual, western world. Much like Elvis Presley did to early rock 'n' roll in the mid 50's, or the Beegees with disco in the late 70's.
Needless to say, I think its pretty cool that they were still able to find a place for that 70's blues-rock in today's world. That in itself is a huge accomplishment, whether you like them or not. But wonder why they're only on dad rock stations; it's because they're just not cool like Led Zeppelin was in the early 70's. They're not pushing any boundaries in rock, and they definitely are no better than Led Zeppelin was. They're no more than a fond recollection of the past.