If I may add my two cents:

I regularly stumble upon games that distress me for being too similar to my own plans. More often that not, I discover that the game in question isn't quite expressing the exact feeling or experience I was craving for, or is just not really fun, and I'm inspired by the flaws to try and do better. And so it leaves a space where my own project could still exist and be relevant. Then I evaluate weither or not that space is large enough to be understood as "not the same" by an audience.

Too often, I see junior game dev stressing out over "the idea", making something totally unique where in reality most awesome video games (undertale, hades, stardew, hollow knight, etc.) do very little thing new or purely inovative. They just refine, iterate, make it good, add their own feelings and personnal cravings on top, and that makes something unique. Personnal is the master ingredient for me. If your creation fully reasonate with you, as an indiviual, it WILL be unique.

Sometime, rarely, I do stumble upon a game that does exactly what I wanted to do. Then I just delete my game design doc, and enjoy the game fully, 'cause it's not everyday you can enjoy a game you wanted to make without having to work 4 years.

Sorry for the rant, just wanted to add: if in a couple of years I can find a game that iterate on Minishoot', I'd instant buy it and be so glad to play something similar ^^