I think it is better to grind out the military levels until you can get to holy knight or higher easily, then on a fresh run, build up to the high income tier and use the money to quickly raise your mana channeling level so you can move through the magic levels more easily.
Disclaimer: I have not tried this method yet
not quite, I kinda got bored so I switched, but I am reeealy close, and I will say it does kinda work but you need to grind and drind levels into all teh useful things like bargaining, strength, ect so that you don't have to sit and wait for 4 minutes for one level when your trying to grind out for the magic line. Another thing I found sueful was kinda just having the tab pinned and setting the skill to one that's typically hard.
like, for example;
Bargain's max level is 30, while all the other skills have max at lvl 75+, so I place my skills training on bargaining for one full run and go like that until i'm satisfied, then do a few true runs micromanaging all the things. Rinse and repeat.
It can get tiring and repettitive so idk if that's the best way to do the level grinding instead of just playing the game slightly different each time (which, I'm sure is the intended way for you to play the game) to get a couple of levels higher than the max level.