I mean Sakura's abilties arent really Infinite Magic and she can't/doesn't do much with her imaginary elements. While she has a limitless amount due to the grail, her output is more limited. With her imaginary elements basically being shadow monsters in practice.
Meanwhile Rin managed to create the Jeweled Sword which puts her on par with Excalibur (along with effectively infinite magical energy like Sakura) and in Case Files: Adventures, manages to replicate noble phantasms