Sure Montella had a luckier start, but a that doesn't say much of what the season will be. It's not worth talking about luck after 8 games.
It's obvious that both coaches have been influential tactically, but in a different way.
First of all, Miha spent 3-4 months of his time with Milan, to choose the formation and the tactics that fit best with his players, while Montella is spending the same amount of time to make the players fit the formation and the tactical ideas that he had chosen at the beginning.
The former sometimes is more efficient, but doesn't allow a coach to fully express himself with the team. Also, the second is the best way to push the club for proper signings and to make players that are not willing to adapt to go f. themself.
Usually, all the top coaches chose the latter way. Conte was probably one of the few in recent times that earned a huge reputation with the former.
A big difference that make difficult to compare Miha and Montella, is that current Milan is a better team. Most of the player have improved in someway, the youngsters have more experience, 2015 summer signings like Kucka and Bacca have got more accustomed to the team, other players like De Sciglio and Paletta have better form.