Being a boxer means boxing. To say Mayweather is a more skilled boxer than AJ is absolutely correct. In this case, boxing skills have been separated overall strength. That's how I see this whole sword skills vs strength debate.
When we say boxing skill, the first things we consider are (I found these just by a quick google search: "boxing skills" lmao) boxer's stance, the jab, the cross, the hook, and the uppercut punches, etc. By skill, we are talking more about techniques than basics like speed, stamina, etc, IMO.
Irl the sword skills means different types of cutting skills, yoko geri, kesi giri, overhead cut, etc. These are very basic in One Piece standard and even fodders in One Piece can do such things. In One Piece verse, I would expect some outrageous shits like flying slash, which are severely lacking. Thats why I wrote this part =>
There is only one skill exclusive to the "pure" swordsmen
The majority of techniques used by One Piece swordsmen are rooted in various forms of cutting or slashing. Its quite possible that individuals like Roger or Shanks could perform this maneuvers given their strength, skill or agility.
As far as I am concerned, there is only one skill thats exclusive to the so called "pure" swordsmen: the flying slash. This technique was introduced during Skypea when Zoro fought Braham. We have also seen Zoro imbuing haki with a flying slash against Monet. Flying slash is something that probably requires a certain level of skill and I dont see Shanks/Roger replicating it without any practice. However, the haki emission strikes (e.g. kamusari) from Roger/Shanks have a similar function. Is flying slash truly necessary for a swordsman who has haki emission strikes in his arsenal?
Another technique that could potentially be exclusive to "pure" swordsmen is the "iai" technique, which involves drawing the sword quickly and striking in one fluid motion. Zoro has used this technique with his Shishi Sonson attack. However, going forward, I dont see any scenario where a fast draw would impact the outcome of a fight.
Its like the difference between slam dunk and kuroko no basket. Slam dunk is realistic, so an elite shooter like Mitsui can make 3 point shots. Making 3 point shots in kuroko will probably not counted even a skill, it will be counted as a basic. In KNB, we have skills like emperor eye, misdirection, invisible pass, etc.