What Roger did could be done with many weapons as far as we've seen, and where your reasoning fails is that this isn't about Zoro and Roger both doing something that isn't necessarily swordsmanship but Roger not doing something Zoro does on a regular basis and is indeed swordsmanship (relying on your swords as a main source of cutting power, and I stress "cutting" as it's the main point of the debate you open with).
Your reasoning will only work if we accept that what Roger did wasn't just sending a blast of haki (I assume) through his sword as catalyst but actually slashing with it; if not the case, then the sword is virtually irrelevant and therefore hard to talk about swordsmanship. And, sadly for you, the whole point of debate you referred revolved around discussing whether what Roger did was or not a swordsmanship technique.
In other words, for your comparison to work we need to accept your point of view to begin with but the debate is about whether that point of view is accurate or not. Therefore, your logic is ridiculous and your thread absurd.
Again, not saying Roger wasn't a swordsman, but I'm honest enough to not accept idiotic logic. For all we know, Kaido has been doing what Roger did but using a blunt club; I mean, Oden wasn't even slashed by this "cut" with Ace.
Today we will talk abou Roger and his attack Kumurasaki .
• As one friend of us here said @Chaves Roger didn't use a slash nothing about swordman ship he just sent an air bar or like what the VC described ( canon material ) a shockwave .
As you noticed that VC described that with a shockwave , Hmmm interesting now let's check Zoro sending shockwaves around :
Nitoryu style :
Manga panel :
So as mr @Chaves claimed by saying Roger isn't a swordman because he sent an air bar which called a wave by VC which according to him a swordman wouldn't do it but Alas we have Zoro sending shock waves around with a named attack not cutting ppl by it