Some of that "adopting" was taking old blues riffs and lyrics whole cloth and incorporating them into larger compositions. It wasn't limited to the level of "concepts." And it wasn't done commonly accepted form of covers, but of literally stealing the music and failing to give credit.
The fact that they stole others' work - or "interpreted" it, as it were - really doesn't make me like them any less. That was my point: they were actually a gateway to many new types of music for me. It's kind of what makes rock music special anyway.
I love LZ and do consider them to be the finest rock band that has thus far existed, but you must acknowledge that the versatility and identity you attribute to the band now did not exist when they were 20 years old.
Even performing a truly credible Zep impersonation is worthwhile to me because it's so difficult. Of the many that try, the vast majority fail. I don't think Chuck's point was that this band is comparable in quality to Zeppelin or will ever be.
People get very touchy about LZ comparisons and I find it kinda funny.