I don't think it's a bad showing from Shiryu but his presence this fight in comparison to Aokiji clarifies a bit, like Aokiji being portrayed as worthy of all of Garp's attention when they're going toe-to-toe whilst Shiryu, who's definitely a deadly fighter, even with the drop on Garp due to attacking his pupil, couldn't stop Garp's assault and instead got taken out.
Honestly nothing bad from him, he went in, used his fruit and swordsmanship to land a good blow but was handled quite quickly and easily by Garp when he had his hands on him. Shiryu will show us what else he has in store as far as his fruit and blade go but he's not a huge issue for Garp in a clean 1v1 (Shiryu's a pirate with ridiculous bloodlust anyway so not fighting fair isn't really a knock on him) whereas Aokiji is.