Sorry to break it to you, Kye, but the bosses in Kill the Shadowlink are definitely not what you should strive towards making.
This, Shadowlink bosses strive in production value, but they're not amazing bosses from a design perspective.
However, you have to keep in mind that none of those games are their creator's first games. You have to make some shitty games before you can make good ones, that's just how it works. Everyone gets better over time, and if you don't believe me compare Dallas to Ghost Realm and tell me that's not the case.
You have to start somewhere, and to give up on something meant to be fun is unfortunate, so try not to beat yourself up over it. The same applies to any hobby, not just fangames.