WOIIFTM is the weakest Mothers album.
Innervisions is a Stevie Wonder contender, but naming Stevie Wonder at all in an all-time classic rock poll is pretty weak.
Same thing really for Sly and the Family Stone.
Almost nobody considers Beggar's Banquet to be one of the top 2 Stones albums.
And, of course, Meddle.
The above list was so poor that it doesn't even merit a response to the poll, IMO.