In the role-playing game supplement, Moria: Through the Doors of Durin, there is a section on the Balrog of Moria which makes some curious statements about Balrogs in general:

The Balrogs were tools of Morgoth, and obeyed his will in all things. They had, it seems, little in the way of desire or ambition of their own.

It is possible that the Balrog has no will of its own, for it existed to serve Morgoth, and now it is only animated by blind, reactive hate - it will strike back at those who trespass in its domain, but has no impetus beyond that.

The game this is for, Free League's edition of The One Ring, is generally pretty well researched as regards the lore, but of course it chooses to add its own spin and creativity where it's necessary to help the game.

I'd not come across this conception of Balrogs as essentially empty vessels of Morgoth before, and I was just wondering whether it has any basis in canon, or in the long history of Tolkien changing his mind about how things worked in Middle-Earth?