If you're going to keep calling it a Deck, you may as well consider making the actual words cards in a deck. For the most part, this would mean that you only have assess to 7 or so words, likely overlapping, in the beginning of a battle, and would either regain them at a specific rate (1 per turn, maybe spending an action out of combat to gain an extra that turn) or through a specific action (You draw back up to 7, or draw 4 or so cards unless/until you reach 7, if you cast no magic in a turn). This would provide another balancing factor, as not only would rarer, more powerful cards in your deck be harder to find, but so would the combos. Then again, this would provide a moderate factor of luck to battles, which could end up being unfair/removing skill from battles to some degree. Then again, this is an RTD we're talking about, so it might not matter too much.
Have you considered words/cards that aren't simply concepts usable in spells? For example, one called "Focus" might be usable to strengthen the next magic spell the user casts, maybe in exchange for taking up a turn. There's also the idea of multi-concept words, such as a combination Dragon-fragile word, that could bind weaker words into more usable units and, in this case, provide a debuff to a more powerful word to balance it out? Lastly, is there any way to have a choice in hat words are makable, or otherwise affecting the word output of hexes? For example, forging advanced chemistry sets so that an alchemical hex can better produce its words (Acidic, Vial, and Poison, for example), or maybe allow the production of a new, stronger word (Maybe Transmutation, Fusion, or Homunculus). Ways of upgrading a Hex might be through purchases via currency and/or words (Providing Glass and Pipe words for the alchemic hex), the constant supply of words as a more continual price (Providing an amount of Gold or Wood words on a daily basis, maybe), through a mission of some sort (Steal the secrets from a rival alchemic workshop), or simply via having certain other hexes (That second alchemical hex you got is working with the first one now, and they've figured out more efficient methods).
Lastly, does the mage itself gain any benefit or effect from using the same word/combination of words over an amount of time? If my mage that starter with Wind, Bird, and Spiral, for example, was able to get and use a continuous supply of Wind words, would they get any better at it? If they often used Bird words with Fire words they obtained to summon, well, Firebirds, would they get any better at that? If they often used Spiral, Confusion, or Illusion words to confuse their enemies, would they get better at that?