But if you draw a cremation on turn 1 instead of an air tower, then it results in lower air quanta.
Take this example. In one deck you make mark fire and replace the cremations with air towers, and in another you keep it the same.
Deck 1 Draw: 7x air tower, mark of fire
Deck 2 Draw: 6x air tower, 1x cremation, mark of air
Deck 1 Quanta After Turn 1: 14
Deck 2 Quanta After Turn 1: 13
So you see, if you replace the cremations with air towers and change mark to fire, in any draw where you WOULD have drawn a cremation on turn one, you will end up with a single more air quantum overall.
If you WOULDN'T have drawn a cremation, you lose 1 air quanta every turn you wouldn't have drawn one. Of course, then you run into the problem that you wouldn't have drawn a cremation so you wouldn't be able to explode the gasses anyway
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Overall, mark of fire is more reliable and can sometimes actually result in MORE air quanta.
Finally, a single cremation is sufficient, and if you happen to draw more than one that card is useless and redundant. At the same time, you need 3 in the deck so you draw at least one early, so you NEED to risk having more than one in your hand. Risk isn't good.