Yes, good thowers may be able to break your mark, but if you force them to throw it at a bad timing, even if it is a break throw, you might force a turnover eventually and that is a win for the defense

Personally this kind of marking defense is just an optional adjustment. You may want to try it tho to some specific throwers who love and you know that they just cant stop throwing hanmer haha

I think its a team decision if you'll try to implement this. Usually you do this flat mark or force middle in some cases to teams that are dangerous to huck plays. Basically you want the throw to be difficult in a way (IO or curvy long throw) if they still want to do hucks and hope that you may force a turnover or hope your teamate to make a play on the disc.