Jack just must have been really tired of the comparisons and criticisms and lashed out unfairly.
While I like about half of what The Yardbirds released, I have great love for what their three greatest guitarists would become and record.
Cream was a brief, shining moment when compared to Led Zeppelin and Clapton's long and influential careers. No disrespect meant towards Captain Jack Bruce.

Wings on the Pig Wrote:Why the hell would it be Eric's idea for Jack Bruce to criticise Led Zep?

Boom, boom!

(Although, jokes aside, Eric has made it pretty clear in his biography he has little opinion of LZ either.)