They’re still one of the best from that era.
In all seriousness.....they rarely just recorded an already existing song and called it their own, even changing it. Levee is one of those they did that with. They made it their own style and it was great. I don't see anything wrong with the creative juices doing that. LZ took a LOT of inspirations (Celtic, English Folk, Delta Blues, Bluegrass, Welsh/Mystical Druid crap) and fused them into their material. No doubt the dudes were excellent at their craft, as evidenced by the yard birds before that.
FYI - Mississippi Delta music ALSO took pieces of other music influences from Europe and Africa. Just like Country and RnR did in the 50's.