I don't know of any quote Brooks said where he admitted the copied LoTR item by item, but I do know Lester Del Rey (his publisher) say he wanted to have Sword of Shannara be Tolkien-lite. A book for the masses, because by then Tolkien started to wane in popularity (from the spike during the 60s), and let's be honest, was not an easy read. Some folks consider Rey and Brooks with saving the genre by creating a novel that could actually be easily read. That was the intent anyway.If it is possible, can you find a quote? Seems like that would go a long way towards putting this to rest.
FWIW, IMO one can make a recreation of someone else's work, make an allusion, do an homage, or create a spiritual successor. All will be identifiably similar to the thing they are in reference to, and there isn't always a direct correlation between which category the new products is and how similar it is to the references work (one given homage may be more similar than a given recreation, the other less similar).
On a side note, no one accuses George Lucas of ripping off Tolkien either, and Star Wars is the space version of LotR, and came out the same year as SoS.