well, in fact your reasoning isn't correct at all, there is no match between these two cases. arab ulama did not endorse deobandiyyah on their kufr, they endorsed them for presenting correct sunni aqidah to them. deobnadi kufriat are present in their books to date; where is any evidence on the incidence that dhahabi mentioned about imam ibn furak rahimahullah without any reference? it is a clear fabrication as sidi abu Hasan noted. when great hadith masters are the students of imam ibn furak and they don't mention anything, then what is the basis to take it from dhahabi or ibn hizm who came many many years later. if ibn furak's rahimahullah execution was a true story then his disciples would have known that very well, it is not something that could have gone unnoticed, or if they had brushed it under the carpet- al iy'azu billah.