Sent them invites on their message walls.
As explained previously, the anime adaption was overseen by the author, which makes it secondary canon (Gotōge-san is involved in checking over the scenarios, character designs, settings, and overall they are intimately involved in the anime adaptation process. I was in constant contact with Gotōge-san throughout production. They actually have a great deal of trust in ufotable, so it was less about requesting changes and more about giving them useful advice to make the best work possible. In my opinion, it was a great working relationship.). And the manga panel still shows dodging multiple attacks in succession. To add another manga FTE feat, Genya's mother was a newly-transformed demon, and she slashed five of his siblings and jumped to the ceiling in front of him before he can perceive it (and considering demons usually go after their loved ones first, she probably haven't eaten anyone yet).
Many instances of 'Talking is a Free Action' are unnecessary but are just for emphasis. The Swamp Demon has FTE feats by virtue of fighting Tanjiro and Nezuko.
Zou Hakuten has comparable speed and Mitsuri could counter a punch attack for example, however Mitsuri was thinking of retreating as soon as she beheads him and lands on the ground, however a slower invisible AoE attack hit her after she beheads him and before she lands on the ground. For you to claim an outlier, an event has to be completely and irreconcilably inconsistent, however the event here is perfectly coherent.
Dragon Ball is believed to be MFTL based on multipliers,
but there are only a few questionable Relativistic/FTL feats and statements we can scale from before Super (also, Kid Goku dodging lightning is anime-only filler). If you believe that subsonic antifeats can be excused if there are various superior feats (i.e. lightning feats), then wouldn't it follow that we take the superior feats and agree to disagree on the existence of low outliers?
If you are insistent on denying something extremely obvious for some reason, Genya's page in the databook states that the gun is made from Nichiri. Breathing techniques can be used to make Nichirin swords stronger, extended slash range, create shockwaves, create illusions, etc. Considering that vastly lesser demons to Kokushibo can casually slice through Nichirin swords it is absolutely implied that Sanemi made the gun stronger when he blocked his slash with the gun, and considering that massively slower demons to Kokushibo can block the bullets it is absolutely implied that Sanemi made the bullets faster. Likewise, it is implied that Gremmy made his guns and missile launchers fast like his other attacks even though it is not stated.
Nichirin swords and Demon Slayers existed long before the organization learned about Breathing techniques; the different sword forms of the Flame/Water/Wind/Stone/Lightning Pillars were likely made to fit the different properties of the Nichirin blade, and when Yoriichi helped them modify the Breath of the Sun into a new Breathing system (since most of them can't use the Breath of the Sun) they modified it to fit their strengths and therefore the sword forms they are best with.
Yoriichi had a black sword that turned red whenever he fights, Kokuchibu also stated that he thought only Breath of the Sun uesrs are capable of changing the color of their sword into red. The supposed successor to the Breath of Flame (meaning he should have learned it) mentioned that a Nichirin sword won't change color for him because he needs to further improve his sword skills first, so theoretically Genya (who wanted to be a Pillar) should get a color change if his combat skills are good enough; the color change seems to be a mix of elements, such as personality (since there is a "what color suits you" flowchart in the databook) and combat style compatibility and Breathing technique compatibility.
If Tanjiro was getting flown upwards, and the sound attack was flying downwards, then Tanjiro was flying toward the attack. Therefore there is no contradiction, especially since Tanjiro described Urogi's flight speed to be fast. A numb and weakened Tanjiro, who is crawling and trying to get energy to get up, would need a lot less effort to swing his arm than he would need to stand up and run.
I said the cross-section was uniform at the shape of roundel slices, the angle of cross-section to be more specific which is what is relevant for the number of slashes. The only 'chunks' I can see looks like a tail wagged away from the screen and a fish head turned away from screen, and even if they were chunks they have the same restrictive cross-section angle which means that Muichiro was inefficient in his cutting and increased the number of slashes.