Gabriel, the theory of Mughals being "descendants of Mongols" is no "nationalist rhetoric" but just a universal theory. It would be natural for even an uneducated anti-Mongol person to think so considering that the world Mughal means "Mongol" and they look so similar.
I agree with your basic point though- the cultural heritage was more important than the blood.
For the matter, a large sector of Uzbek society is descended from Mongols according to the book Taliban by Ahmed Rashid.
"Every body here must understand that the Mongols at that time were EXOGAMOUS: there was no problem for them to take foreign women as wifes. So stop the f*ck about blood and lineage, and just consider the cultural heritage of the Mongols: nomadic invaders liked to be called "Mongols/Mughals" because it was a sign of respect for the great Mongol conquerors. Just like the German nations respected the Great Roman Empire. That's just as simple as this!"
Please don't swear.