Unless you can find a card that you feel you really need to replace Falling Away, I would disagree with the other Prof on this one. In my experience with Heroless, the goal is to wear down their offense until they have nothing left to attack you with, then come in for the kill. Even against a solid defense, people will be able to rescue one or a few LS's if they can catch you unprepared (which sleeker decks often can). In order to beat a defense like this, an offense will usually need at least 5-6 effective battle winners (since you have banding and ways to bring in more defenders after the first one is discarded). If you're able to neutralize one of their successful RA's with FA, or at least have the possibility of doing so, then I'd say it's more worth it than most any other card.
As to the other Prof's points:
1) Yes, maybe a fair amount of times the opponent will get GoYS first, but I'd say the potential reward is worth the risk.
2) An early CBN Zeal/AoCP can easily get an LS from this deck, especially if the initial draw is mostly forts/arts/GE
3) You don't need LotS up until you are ready to Grail, and at that point, you will either have used FA, or no longer need it.
4) I can't think of any other card that has the potential to be as helpful for this deck as Falling Away.