I appreciate the thought you've put into the control scheme based on playtester feedback. It's great that you're prioritizing what works best for most players.
From my experience, many games using WASD also incorporate Z, X, C for actions, especially in strategy games where quick reactions aren't crucial. Have you considered allowing both WASD and arrow keys as options? In my experience, providing choices often caters to a wider range of player preferences.
Another idea you might consider is implementing full mouse control (clicking tool icons to switch and clicking the grid to dig). This could potentially make the game more accessible, even on mobile platforms.
Regardless of the control scheme, I found the core gameplay enjoyable. It's clear you've put a lot of effort into creating a fun and engaging experience!