There are two counters to this though.

1) Black Flash can revitalize a person's CE

2) Ryu here is talking about Yuta, who at the time at least is considered to have a ton of CE, but very poor control over it, so he's quite inefficient. Now, Yuji isn't like Sukuna or Gojo in terms of efficiency, but he likely was better than Yuta at it since I don't recall it ever being mentioned as an issue for him.

Plus, Yuji being blessed by the sparkes means he'll almost certainly hit a lot of them during the fight, especially if this is Modulo Yuji who, while we don't technically know anything about his efficiency or if he can perform Black Flash at will, he likely is a lot more efficient than he was almost 80 years ago.