It would NOT work with 40+ cards. For it to work, you need to be able to deck out, or at least come close. This is because you NEED all 6 fire lances, unless you get lucky and your fahrenheit does tons of damage. With 40 or more cards, it would be impossible to deck out; assuming you wait 5 turns, there is 27 cards left. Then assuming you get all 6 sundials, and draw two cards per turn, there is still 3 cards left in the deck. And that is optimized. You very likely would be left with 6-10 cards left.
With 6 fire lances in a deck, there is a high probability one will be in those last 6 to 10 cards.
Also, about your theory that light towers either work or don't work, I would argue that too MUCH wouldn't work, and too LITTLE wouldn't work either. The only purpose adding in another light tower would serve is to have a higher chance to get it earlier.
The deck works without a light tower, (I just beat Hermes when I got the tower first turn but then he exploded it. I still managed to get all my cards.) it just works better with one
.
Last thing:
1 Light tower, 16 Fire towers > 2 Light tower, 15 Fire towers > 0 Light tower, 17 Fire towers. The second light tower only serves the purpose of getting a light tower earlier, but the first lets you hasten each turn. So, in effect, one light tower is better than one fire tower, but two light towers is not better than one light tower and one fire tower.
Oh and sorry for the long post. Again.