Heavenly_Raven
From the story so far, I think author is approaching the MC's ability, as an opposite of Bam, where Bam is exceptional in Shinsu control and improves his physical combat skills throughout the series, it is the reverse for Liu. It does make sense, since he has little idea on the field, had no formal training on it, and focuses mainly on martial arts for fights, based on his previous life experiences from a Wuxia world. His training has also been, and likely will be centred on achieving his peak as a martial artist, which is literally his goal in the Tower. MC is by no means "not talented" in Shinsu manipulation, he is just way more oriented towards Shinsu strengthening and augmentation for physical combat. He sees it as an excellent feature to further his pursuit of martial arts, and even Adori admits his learning curve about shinsu to be so high, that he would surpass her (the most talented non-irregular) in course of climbing the tower, which, by her standards, should be extremely fast. Knocking him for not having the Shinsu control capabilities of a Wave Controller when he's just on the 20th floor as a Fisherman, would be like knocking Bam on the 20th floor for not having the physical capabilities of the Ha family. Irregulars may have nigh infinite potential, but they still have to start off on a position that suits them, even Jahad and the 10 FHs did that. Liu entered the Tower to pursue freaking martial arts, not make light shows and shoot pew-pew beams with Shinsu. Now that he's introduced to applications of Shinsu other than physical combat, I think author intends to have him master this throughout his climb, in order to further complement and enhance his combat prowess overall, and train in something other than the Wuxia power system. Tl;dr: MC isn't Bam, they have different fighting styles, one is a special attacker (Alakazam) while the other is physical (Garchomp).
Your story deserves my power stones. Looking forward to MC continuing on his path. Maybe his struggles will lead him to a truly great, unique and unmatched achievement in the Tower. Really wish you can continue writing this for a long time, for, as you no doubt know, there is a lack of quality, long-running ToG fics all over the internet.