Thank you for your comment. As there are many levels into this spectrum, it was to hard to make a appropriate study for this game, because we made it all in just a week for a game jam. We are working on another videogame with maths as main topic, with different levels of difficulty, and we hope that this problem gets solved for this new game. On this game, The Wordland Scape, we eliminated the competitivity not showing a clock and not comparating the final score, so it doesn't happens anything bad if the player just find a few words, so we tried with this to make a videogame not frustrating and with this, the level of difficulty decreases a little. But, obviously, for making this game better, we should study with professionals and testers so we could adjust the hardness better.
Thank you again for your comment, we will consider it for our new game :)