There's no calc for Sundown, so the only speed given to him will be somewhere between
34.3-171.5 m/s or 76.7-383.6 mph
While Hitori Tachibana/Oniwakamaru are far superior to Kasha who could outspeed a car going 125 miles per hour = 55.88 meters per second -
https://i.imgur.com/ASMi5Rk.png
And doing the leap which led them high into the air -
https://i.imgur.com/jro2YZU.png
They're separated by a distance of
dozens of meters, which can be instantly reached by HT as his Speed isn't limited to only Attack/Combat/Reaction, but he also has Travel as seen with the other examples above while Sundown only seems to have one of the 3, if not all of them and certainly not Travel, based on his Profile (His firearms should be this fast. Can dodge bullets being fired at him)
Even if Sundown shoots his bullet at him when HT tries to close the distance or goes up into the air, it can still be deflected as I said before then he'll be pressured to CQC immediately after (Since Sundown fights primarily with his guns, and it's not even taking into account HT or the others disarming Sundown by attacking his hands which will be carrying the guns) and even if HT is hurt, Sundown will still have Oniwakamaru to deal with, who'll pressure him even more in CQC and that's not even taking
Benkei into consideration who'll increase the pressure on Sundown even more
And they're located at Central Park, New York City, so there's plenty of stuff that Benkei can use to attack Sundown while they can dodge his Molotov Cocktails by going up if Sundown tries throwing it at them, so it'll be a waste for Sundown if he continuously does that since his supplies are limited
Even if the MCs hit HT, he won't really be feeling any damage as seen with Oniwakamaru walking away with it just fine -
https://i.imgur.com/NAHXfxZ.png
And this is HT prior to Oniwakamaru taking over saying that he had burns from it, but it's gone as it's healed, while also before HT had full control of Oniwakamaru's power, so he isn't gonna get affected by them -
https://i.imgur.com/niLwMIY.png
Sundown can still win if he can pressure Hitori enough to deal with him before he can summon Benkei, which is unlikely because he'll be using Iwatoshi, which houses Benkei's soul; or Oniwakamaru but that's also unlikely since he'll be coming out if he deems HT to be in danger. They both can be unused if HT dies before the instances explained above happens, meaning Oniwakamaru and likely Benkei will die if HT dies as their souls are together inside him as of now
Count me in for Hitori Tachibana - 7/10