Sentence:  If the change , at first sight , seems minor , we may recall that it took the Italian painters about two hundred years to make an analogous change , and the Italian painters , by universal consent , <WSD>were</WSD> the most brilliant group of geniuses any art has seen . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)