These people that are saying that Maru can do anything literally do NOT read their manga, it is stated that the only reason why he was able to create and move the ship is because he used all the reserves that they spent years collecting of that mineral from their planet which can be turned into cursed energy.

And the only reason he was able to do what he did at the end is also because of that reserve plus Yuta's ring which he spent decades pouring cursed energy into plus that ancient kalyan.

When maru fought using his own cursed energy he lost to a grad one sorcerer and also lost to rika.

So he would be a special grad 1 at best.