Their music is totally unrelated to each other's, IMO. Everybody has opinions, but in mine - it is only in relation to some inappropriate Donovan publicity spin - trying to gain value by arbitrary association/comparison to Dylan. Dylan was/is a totally independent, even defiant, musician. Donovan was someone who tried his best to be what people wanted.
I also think it's improper to say that any artist is a variation of another. Even in painting one may have studied another but that does not make them a different version.
In music I can't think of any artist (solo or band) that has ever been called a version of another - it's insulting to both. I did like "Season of the Witch" but consider "Sunshine Superman" and "Mellow Yellow"(his two big hits) - give me a break. Dylan has hundreds of songs ranked at the top of every knowledgeable critic's "All-time best" lists. "Like a Rolling Stone" - best song ever - Rolling Stone magazine. Dylan has many, many songs in this category. "Highway 61 Re-visited" - one of the top albums ever (don't remember "ranking"), along with quite a few other biggies. He was a HUGE influence on The Beatles, Neil Young, Jimi Hendrix, Van Morrison, and many others, in fact folk and then rock altogether. Not to mention he's still going very strong (awards and all), although his voice is practically gone. Songwriting his best thing anyway.
If you ask(ed) Dylan or Donovan, I think the videos below will show what the answer would('ve) be(en).
Cohen is Canadian, and has talent but I would put Neil Young above him for the Canadian effort.
Sandy Denny (Fairport Convention) might be a "contender".
Lennon and McCartney (together only) another possibility.
*Probably will add to this (you touched on a sensitive subject).