I really liked the idea of characters having to outsmart each other. Are there any anime similar to this? I already know Death Note and Classroom of the Elite has this but are there any more?
When you go to the anime on anilist and scroll down it shows you recommendations that are similar to the show to an extent.
Code Geass Hangyaku no Lelouch
^ Prolly what you're looking for
If you like war as the main theme, Kingdom is one of the best (altho the art of the first season is quite questionable).
Outsmarting as in, in a battle on tactical, and every now and then strategic level. Politics also get involved.
Kingdom
I'd carefully also suggest Boogiepop and the others. It's not really about characters outsmarting each other, but I got a plenty out of trying to figure out the world – connecting the dots. Figuring out how the characters and stakeholders are connected, etc. There's also a bit of a cat-and-mouse play here and there. I could see similar ppl enjoy it.
Boogiepop wa Warawanai
I would have also suggested Promised Neverland and Kaguya-sama but seems like you're already watching them.
My top recommendation is this so you should 100% finish it!
The Promised Neverland
Otherwise this is a great choice as well although it is a comedy, which you might not be looking for
Assassination Classroom
Also if you like Death Note you could try this again? (though I completely agree that the characters can be less than immersive)
The Future Diary
Depends on why you liked it, if you liked it because of the tactics and strategies applied by the characters then I am sure there are plenty but if you liked it for the Main Character... then I am sorry but I doubt there is any other MC out there like Kiyo. You can just read the light novel but other than that there is almost no Main character like Kiyotaka probably, if there IS then I'd wholeheartedly watch that show. The manga sucks or so I heard so LNs are the way to go
They have the same school structure Baka and Test Summon the Beasts