I don't have a real opinion on the thread's main question yet, but I want to weigh in on one of the arguments.
Ryoma was constantly trying to beat Prince at his own game. This became evident when he used his Allez! return and was pissing him off, and at the last set when he was waiting for the chance to return the SSS doubled. Why didn’t he use TnK or other strong moves like his Glowing Drive B? Or the applications of the glowing shot in his other techniques? To me he would have had a much easier time if he indeed did use them, chances are he didn’t need to, therefore he didn’t use the 100% of his arsenal.
One of the reasons might be the way TnK explicitly got re-contextualized in Yukimura vs Tezuka. Up until that match, all we knew was that it provided some sort of stat boost to the user. Back in PoT 378, Inui even suggested that it simply builds on Ryoma moving Hyaku Ren's aura to different parts of his body. There was no mention of other effects, though, like Hyaku Ren's doubled return or Saiki's shot count prediction.
In Yukimura's match, we learned of the pressure the aura exerts and we saw how much this affects the way the match goes - Yukimura went from being overwhelmed to winning the set when he blocked out TnK's light. I guess we don't know if Konomi always worked with that in mind or made it up during the semifinals, but for the benefit of the argument, I will assume that this has been true somewhat consistently.
To circle back to Ryoma vs Ludwig, Ludwig did beat Hyaku Ren easily when Ryoma used it on his legs. Ryoma's main concern was even getting the ball back, so maybe in the sense of increasing his own abilities, TnK wouldn't have made a real difference. On the other hand, we saw that Ludwig easily caught up with Ryoma's attacks, so TnK might not have provided enough of an offensive boost either.
Of course that's not the whole picture. But if Ludwig essentially showed that he could deal with the way the aura would've improved Ryoma, the real question is how he would've dealt with the additional effect, the light itself. This might be a stretch, but I wonder if Ryoma opting for Hyaku Ren over TnK could imply that TnK's secondary effect wouldn't have worked? Maybe Ludwig is so conceited that he wouldn't have been taken in by the light. I'm not necessarily arguing that he has higher mental strength than e.g. Dorgias or Yukimura in general, but maybe his personality would've allowed him to pass that particular test more easily.
As for Drive B and COOL Drive, I think part of the problem is that Ryoma was never in a position to use them. Drive B is a move that requires forward momentum, but Ludwig was making Ryoma run from side to side all the time, even when Ryoma was finally able to get into rallies. Similarly, COOL Drive requires a high ball as setup and Ludwig never gave Ryoma any of those either. This is a case where I'd give Ludwig credit for sealing the shots instead of Ryoma choosing not to use them.
It seems to me that the only Glowing Shot candidate besides Hope would've been Twist Serve, but it's again unclear to me if that would've been more effective than the regular Twist Serve he used to set up Hope.
With all that said, I still agree that Ryoma probably didn't play his best tennis, at least during the first set. I also think the reason wasn't Ryoma holding back, though, but his mental state at the time. Before the match started when Ludwig provoked Ryoma, Fuji said that Ryoma was flustered or distressed. Getting aced point after point from the beginning probably didn't help matters. In the end it took Mifune to actively coach Ryoma for Ryoma to change his strategy and focus on attacking with Hope. I reckon he was at 100% either after that or at the latest after regaining consciousness at the end of the second set.
Finally, even though Ryoma won the last game of the second set by copying Ludwig, it doesn't seem like the copy was perfect. Troughout the match, the commentary was that Hope was Ryoma's only consistent way of scoring. I guess in the final set, Ludwig could still stick to his patterns all the way, but Ryoma had to keep changing it up and score with non-repeatable tactics.
This actually ties into the final point as well. Ryoma resorting to Hope again made Ludwig think that Ryoma had run out of novelties, but returning SSS was the final ace up Ryoma's sleeve. I think this should be read as Ryoma saving a trump card until the end, similarly to how he only scored once against Tanishi's Big Bang, and not as him holding anything back. If he had tried to win the whole set that way, Ludwig may well have found a counter to it.
