Who is Guru ?
The person who give teachings to their disciples.
Now Guru nanak ji and other ten gurus are Gurus for their followers ,but they were Bhagats!!!
How??
They were Bhagats for akal purkh (almighty God) . As they preach akalpurkh .
Likewise Guru Ravidas ji preaches almighty , therefore he was bhagat for him not for us.
Now Guru Granth Sahib Ji is Guru for all of us . And granth sahib ji has bani from many of Bhagats . Guru Gobind Singh Ji give it place of last guru . It means the person who has bani in the Guru Granth Sahib Ji treated same as Guru if some blame Guru Ravidas and other
It means he or she blames shri guru Granth Sahib Ji .