I guess it all depends on what you mean by “worst”
Freebird is overindulgent, but competently structured (as mentioned above, hard to do with 3 guitarists) and pretty well executed
Stuff by Jimmy Page is known for having a little “slop” in it - he was never precise, but always captured an amazing feel. I put Chuck Berry in the same category - I was just listening to a bunch of his tracks, and it always sounds to me like his hands are too big for the guitar neck - but I love his stuff.
There are a number of solos that are frankly incompetent - the lead break in Louie Louie by the Kingsmen comes to mind - but that is part of their charm.
George Harrison had wonderful taste, but didn’t have the assertiveness that I look for in a lead guitarist - is he worst? Nah, but I can’t think of many leads that stand out, except for being a great fit for the song. (I worship the Beatles, btw)
What about Nirvana - what comes to mind is the lead break on the Unplugged version of “The Man Who Sold the World” Cobain starts off the break with a honker of a bad note. I respect their music (or in this case, Bowie’s) but it’s just a mistake, plain and simple.
I agree with the “dweedly dweedly” solo on Enter Sandman - cliche, and the lick he plays when they change rhythm parts always sounds off to me.
And don’t get me started on the Dead or the Doors. owlstretchingtime and I seem to be in the same camp, but I know lots of folks love them.
So, no real definitive answer. I guess, if pushed, I would nominate Vernon Reid of Living Color’s lead in “Cult of Personality” - both leads, in fact. I know he is a big rock/jazz/fusion guy, but as a guitarist myself, I find his stuff to be a blurry mess of notes with no structure, melodic interest or anything. Just slop to my ear, but since he is pretty well respected, I write it off to being over my head, but in my heart of hearts I think it is simply bad.