He is in fact not a hard counter to this.
How is EMIYA NOT a Hard Counter to Senbonzakura Kageyoshi?
EMIYA rarely if EVER pulls out UBW precisely because it's not a good combat weapon
....

Man, that must be some absolute good weed he's smoking because not only is that not true in canon, it's not even true in F/SN

Shirou's win against Gilgamesh was precisely due to UBW not only copying Gilgamesh's weapons faster than he can draw them but also materialize and destroy his weapons before they could even become effective:
Here, he final leg of the battle begins inside Shirou's Reality Marble.
Here, Shirou counters Gilgamesh's longsword with his own copy of it, they both shatter.
Here, Gilgamesh goes for a curved sword, but Shirou pulls the copy he has of it at his feet out to attack Gilgamesh faster.
Here, Gilgamesh fires from the Gate of Babylon, Shirou counters with his own attacks.
Here, Shirou forces Gilgamesh to retreat, Shirou closes the distance and slashes at him.
Here, Shirou crashes more of his copies against Gilgamesh's appearing Noble Phantasms.
Here, the instant Shirou sees one of Gilgamesh's Noble Phantasm, he reels the copy of what he saw in to attack with.
Here, for Gilgamesh to keep up, he must counter Shirou's swords by breaking his own against Shirou's.
Hell, it's the entire point of why Gilgamesh didn't want to fight EMIYA in the first place and tried to gank him and Shirou at the Mansion:
Here, Rin surmises Gilgamesh sees EMIYA and Shirou as threats, that EMIYA would be a match for Gilgamesh's Gate of Babylon.
(You can't even say that "it takes too much energy" because EMIYA literally uses the shit twice(The latter when he was less than 1/10th of his overall power) and still takes the damage he gets from Gilgamesh and saves Rin's ass from the Mountain of Flesh... while being Masterless and not even recovered since his fight with Cu and backstabbing Medea.)
the only reason it's so effective against Gil is because Gil mindlessly spams weapons out of GoB versus using it any tactical manner.
I see we are just rewriting history now...
He's basically mixing up that Shirou cannot defeat other Servants with their own weapons but Gilgamesh because Gilgamesh can't actually truly master the weapons in his vault = Gilgamesh just throws shit out with no plan whatsoever which is false as fuck. Shirou explicitly had to keep Gilgamesh pissed off and angry or else Gilgamesh would immediately reorient himself and demolish the boy:
Here, Shirou asserts Gilgamesh will win if he regains his composure.
This was AFTER Gilgamesh got his arm cut off too.
Sebonzakura is something that Byakuya has mastered and learned it also is not functionally the same as GoB the man can literally control every petal and where it goes and can also just outright protect himself with it against anything EMIYA has in his arsenal.
...Gilgamesh and EMIYA have used GoB and UBW for defense, hell, that's what Shirou did in his fight against Gilgamesh and vice versa. This is also dumb as shit because he's ignoring the fact that EMIYA can ALSO attack and defend at the same time due to how UBW operates.
(He starts with all of these petals btw this isn't a GoB case where he has to keep producing them.)
...Uh, yeah that doesn't stop EMIYA from being able to see them coming and if anything, that makes it WORSE than GoB because Gilgamesh can have portals appear above, below, behind the person or literally within pointblank range.
That's not even accounting that Byakuya doesn't even need his Shikai, EMIYA has little to no answer to 'Senka' for example,
Fucking Senka... we are going to pretend that fucking SENKA matters when the only thing it took down was Substitute Shinigami Ichigo? For one:
Archer has both moved well past speeds depicted in Senka and has dealt with that same shit with Cu(Whose canonically the fastest of any Servant in the HGW) and has attacked in their first fight with well over a Hundred Attacks in less than a second:
Here,
this final exchange has so far only lasted for an instant, but over 100 strikes have been thrown. EMIYA is disarmed a number of times as he marches towards Cu.
Here, though EMIYA's speed is impressive, as Cu disengages, the speed he displayed is even more so.
Here,
Cu had disarmed EMIYA about 27 times, EMIYA managed to reproject one of his swords each time.
(The anime does touch upon this with keeping the number of times EMIYA was disarmed during the final exchange, so yes, they still went into those apparent bullshit speeds, projections and defenses all in less than a second).
Point is, using Senka for a serious debate is the dumbest shit possible when not only did Shikai Ichigo was able to block it while injured to shit, so did BASE RENJI
And the only time Byakuya killed anyone with Senka... was Zommari AFTER he already all but killed the Arrancar with Gokei
unless you genuinely think his reaction speed is better than Post Fake Bankai Renji.
My brother in christ, base Renji stopped that shit in their SS Arc fight:
So unless you are telling me Renji in Base somehow surpassed his Lost Agent Arc self in that instant, you are basically telling me that Bleach Powerlevels are absolute bullshit

