Interesting! That is a point of unfairness against Legacy.
However, I would argue that the solution is to require Standard players continue to face target for the whole cast. Even with Auto Face Target tracking a mob, a cast will still get interrupted if an enemy runs through me, even if they do so somewhere in the middle of the cast and I could have auto-spun to face them before the final cast check, which suggests to me that they intended for characters to maintain facing throughout the entire cast.
I also think that we should be able to spin around in place using right click drag, but I don't think it should allow breaking LoS without breaking cast.