In some ways, fairly balanced, not bad. I'm only upset MC progresses so rapidly from mana manipulation within the body to remote mana mastery and skillshot. It'd be one thing if that took 10 years. Yet he dukes it out with a General at age 8?
Considering that on the back of "I died a mid-20's salaryman, so of course I can run an estate at age 5," it's ... a little weak. I think taking over the territory wholly without his father realizing is the worst wish fulfilment.
I'm willing to forgive most of it because he does get in a life-or-death struggle without realizing it. He survives by a feint and likely upsets the timeline. If the protagonist does struggle and does face consequences for actions, intentional or not, that's better than most of the issekai genre.