For starters, none of the characters you mentioned were my choices.
Second, there are continuities in DIgimon where not only the Digimon have lived for thousands of years, they have perfected their skills as well. Oh yeah, they are not fusions or evolutions either. There are many Digimon who specifically train and engage in sword-based combat and the Royal Knights including Omegamon have clashed swords with them and fended them off or defeated them. So lol at the "no training or skill with a sword". Also, Omegamon and Alphamon DO have those kind of stats as well as hax.
I like how you've completely ignored the question of how they are superior compared to D. To reiterate:
What makes their skill superior to D who as you yourself have listed can accomplish insane shit with just a regular sword? Do their swords possess special properties/grant special properties or are they just plain regular swords?
You are dismissing everything as not being in D's league but can your two choices accomplish shit like that with no outside power, no special abilities, weapons with nothing special about them whatsoever and just purely based on skill?
You say this so I'm sure they must have some good shit:
In terms of physical strength they may exceed "D" (except Kenshin), but with the kind of skill and ability employed by him, strength is meaningless
I'd certainly love some scans or statements showcasing their "superior" skill compared to D. Oh yeah, the lightspeed part of D as well.
You did answer one though albeit a bit indirectly.
Concerning "hax" abilities, is everything allowed or just sword based hax?
They didn't start with hax powers, but acquired them later. This does not detract from the fact they were still Trained and Skilled Swordsman. Their hax moreover complemented the skill they already possessed.
So, other hax is allowed I take it. This certainly raises the amount of potential characters who can beat D.
It's like this. Omnimon X could easily kill Kenshin, but Kenshin is a thousand times more skilled with a sword than Omnimon X could ever be.
Depends on which continuity we are talking about and your definition of what counts as skill. Omegamon X is basically an upgraded Omegamon. Experience with swords, years of training and fighting powerful opponents including "swordsmen"? Yes, some versions possess all that and more.