I also developed a word search game and was interested in a methodology for determining what words are "reasonably findable". The best I could come up without going through the dictionary word-by-word like you did was to use data from actual games played, to see what words were actually being found by the players. Here is the word frequency from about 900 days of daily challenges (about 15 players per day), ranging f…
Also this was a somewhat similar effort to yours, to create the Common English Lexicon word list that can be used on the word game site woogles.io:
https://github.com/Fj00/CEL