Longer words definitely needs to have more incentives like group damage or something like that. I was thinking about having swaps and destroys (similar to the shuffle and reroll) but didn't know how balanced they would be. Now that the game is finished for the jam and I've had some play test feedback I will definitely find a way to add these power ups.
To answer word detection, I used this library: https://github.com/dwyl/english-words. There are definitely some words that might need to be filtered and need to be worked on for the future.
Thanks so much for the detailed input and for playing my game :D