Oh, yes, Louis' ending was something my friend and I also discussed a lot in its bittersweetness. But in the end I imagine he will be happy with the path he has chosen, for two reasons:
Firstly, because in the end it was his decision, the path he has chosen. It was a duty that he has chose, but duty was presented to him as a choice / and option the same way a different life has presented / offered itself to him. But with his father and the burden / exception of the mantle of the Beastar gone, it feels to me it was finally his choice and his path because he chose to, not because it was forced upon him, like it was for the first two thirds of the manga. Without this ability to relatively freely choose, I believe the same path would have brought him resentment instead.
Secondly, as you have introduced earlier in this review yourself, there are many sides to all of us, and while surely a huge side of him, taking over the Group and the accompanying decisions are in my opinion not the sum total of Louis and there is many sides left for him to explore or expand on still in his years to come to find fulfillment and happiness in. E.g. the relationships and activities he'll still have aside from duties, maybe even more so in the years to come if he brings the company to "where it should be" and were to retreat from active duties there.

I never thought of that, but i would be inclined to agree. Now that he is free to make a decision (instead of being forced down a singular path), Choosing to run the Horns conglomerate would now be a future for him, not conforming to the expectations of others, but rather pursuing it because it is what he wants to do and that he feels it is the correct choice.

I would love to see him eventually retire from the horns conglomerate someday to pursue the things that he wants to pursue for noones sake but his own~