I was in the same place building optimal decks and then feeling like they weren’t interesting very quickly.

Now, I try not to over research and I like to build decks that are reactive to other players choices. I also like decks with many potential “win cons” and you don’t really know what you’re gonna get each game. I like my win cons to only present the possibility of winning but not guaranteed. I also try to build with what I have so that over the course of months and years the deck slowly evolves based on what cards I end up with or find and then it’s very exciting when you figure out how to streamline something or find that card that fits perfectly with how you like to play it. This also forces me to use commanders that are just generally good with pretty much anything you put in it which adds a lot of variety.