Very cool game. Very nice game play loop, I can see this turned into a rogue like game.
One of the few games that pushed me towards finishing it. I was able to get to the end by killing the boss.
Two major things to improve
Visual feedback/Animations:
The game really needed animations for the attacks that the player, AI and NPC do.
It also needed animation/visual feedback on when a character/enemy gets hurt. this could be as simple as changing the color of the existing sprite to red.
Also needed some kind of metric of how much health and attack damage I have reached, as I kept upgrading but lost count of what's is my current DPS/health.
Game Balance:
Game starts out kind of hard but that emphasis the idea of the theme of stronger together so the more you hire the more your OP. But that also creates a problem that later on I did not need to attack and even for the boss I just ran around while my 13 knights destroyed him in a matter of seconds. So difficulty might need to be adjusted based on the player level/power.
Also maybe hiring and upgrading can get a bit more expensive so that the difficulty ramps up and it is not too easy to be able to get like 150 gold in one run and go back to do a massive upgrade.
Even with these two things to improve, I enjoyed the game a lot. One of the best games I have played so far (I have played around 60 games). Great job :)
I hope you get to 20 ratings, I have created a post for good games to promote themselves if they have not reached 20 ratings, you can post your game there if you want:
https://itch.io/jam/brackeys-5/topic/1234246/games-under-20-ratings#post-2732277