I played some more after reading your comment, and I realized I missed the controls explanation on the title screen, so I hadn't used the 1-3 hotkeys either. I like drag n drop, it's way more convenient for movement. I was able to experience more fluid gameplay 😁
To help communicate the controls, you could maybe show a message box explaining them at the start of the player's first raid when their crabs enter the arena, and maybe an option in a pause menu to display them and choose their preferred scheme.
This time I encountered the yellow guys and my party was slowly defeated in a matter of 3 or 4 more rooms. I'd say they are the only real threat and they do pack a punch 😅
It took me some time to figure out the icons on the paths you chose after winning are the reward you'll get for clearing that room, and it may not be obvious enough that you have to click on the reward to claim it, maybe a floating or glowing effect would help to make it stand out more.
Also, I preferred some upgrades over others and felt like I had to memorize all the symbols to make an informed choice. There was also some trial and error as I tried new icons without knowing if I would have liked something else better. Short tooltips on the icons could help here.
And finally, some battles seemed to end while there were enemies remaining on screen. All the enemies die at once and the reward appears, but it doesn't occur every time and it's unclear why it does.
I hope that helps!