King Sombra was an extremely bland character, but he also proved to be a consistent and powerful threat, right until the very end.
 
MaloMyotismon is essentially the opposite: he’s the latest incarnation of what is quite possibly the most memorable and charismatic villain the entire Digimon franchise, yet he spends most of his final appearance being beaten to a pulp by the heroes, leading to probably the most humiliating defeat in the series.
 
So what would happen if they fought each other? Whatever it is, it’s bound to be disappointing.