"D" has combat and reflex speed around lightspeed or above. None of those you propose are anywhere close to that. 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. Kenshin is barely super-sonic, Mihawk and others are in the hypersonic ranges. None of which helps against "D" who is vastly superior to them in that regard.
Rey Yan is a trained and skilled swordsman. While the skills he employs are often in the form of special attacks, it was something he Learned and Worked for, as opposed to simply being given. The same applies to Tenchi, who has been trained and drilled in swordsmanship since he was a kid by his grandfather. 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.
It's easy to just find a hax character, throw a sword in his hands and say "he wins". It's not easy to find a character whose actually skilled in using a sword with the power and ability to tangle with "D". Most of those who get mentioned either have hax power and no skill or skill and no power to get the job done.
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.