Theoretically this is true but in reality a road fd intended for a 52 or 53T large ring will work OK with a 44/46 big ring. The shifting won't be the very best but you probably won't notice the minor difference.
Years ago Shimano had the RSX triple group that came with 46/36/26 chainrings and an RX-100 road fd meant for a 52T chainring. It shifted fine with that "mismatched" combination.
You probably can't use an MTB front derailleur satisfactorily with a road crank since the cage radius is too tight and the fd would have to sit too far above the chainring to clear it properly.