Am I right in thinking that one did not apply to become a Professor in those days, one had to be proposed for the post by at least one person attesting the candidates qualifications/fitness for the post.

I do not know if Mackay spoke Gaelic, ancient or modern, he certainly appears to have been able to read, write and understand both.

Was his work questioned at the time by, as mentioned above, the numerous well qualified scholars, or since, as was my query in the O.P.

Thanks for the information in the replies