I think the grid puzzle actually fit the theme of lockpicking, perhaps not compared to other lockpicking games, but in the sense of trying to maintain multiple other factors while adjusting further and further. Though you are absolutely correct in needing more time with it. I failed on the 4x4 constantly, only beat it twice, accidentally, and with luck after resetting it countless times. I should've just not done the 4x4 version. It was an unnecessary door, to maintain the illusion of being lost in a labyrinth, that's where I put most of the 'hard' puzzles. I tried to keep to the idea that easy puzzles introduced the mechanic, medium puzzles (3x3) were for progressing through the dungeon, and the hard puzzles would either be 'another' entrance, or access to one of the three collectibles that would determine the ending dialogue.