The girl was already into MC and there really was no reason to break her mind
If you wanted a route of "discard the core premise of the game to ignore your super powers and form a monogamous relationship with one single girl without using your power". Then sure. Hypothetically that could maybe work. (although in that case you run into the fact that vast majority of "first crush" type relationships do not work and will end up in an ugly breakup or divorce)
But, having a crush on the MC does not mean she is ok with marrying a guy who is a mind controller with a harem of sex slaves.
So he absolutely needed to mind control her.
Also, you have 3 tiers of total control:
1. lover = original personality. only in love with you and absolutely loyal to you.
2. servant = sex slave
3. puppet = mindless
That all being said... it is a bit clunky and immersion breaking for the process to always be:
step 1. break them into a servant
step 2. change them into a lover or puppet.
it should let you pick between lover, servant, and puppet at the moment of breaking.
Calling them LI's is just wrong, they are mindless servants and nothing more, yes you can program to "ACT" like they are but there not. You control every aspect of there lives after you break there minds.
They are not mindless servants. Only puppet mode makes them mindless.
The other two methods fully retain their mind. They are sapient people with desires (that are lower valued then your own orders), emotions, and rational thought. Capable of learning, deducing, solving problems, and so on.