 If you liked
Kenja no Mago
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 ...then you might like
Shijou Saikyou no Daimaou, Murabito A ni Tensei suru
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Two super magicians reincarnated in a world with a "low" magic level. Basically your usual overpowered MCs story. The only difference so far is that Kenja is an Isekai and Shijou isn't (the MC reincarnates within the same world).
Also, both have this initial magical school delepment to introduce the characters, harem included, before jumping into the "fight demons adventure" usual in this stories.
With that said, both are actually entertaining and "better" written than "Shikkakumon no Saikyou Kenja".
So if you like one, you may enjoy the other two. Just give them a chance.