If you look back, you will see that Uryu's potential was second only to Ichigo himself (Ichigo is MC and also perfect hybrid).
- Uryu in the SS arc was able to fodderize captain level shinigami (Mayuri) and i don't think that Ichigo could do same.
- Before using Letzt Still, i'm quite sure that he's power was there around Ichigo's level in shikai (maybe little lower).
- Ryuuken commented that his power in SS arc weren't mature yet and if i remember correctly he even said something like Uryu being able to defeat captain even without Letzt Still, but i could be wrong. And i will also add that Uryu at that time trained alone, unlike Ichigo who had help from Urahara.
- In the Hueco Mundo arc, Base Uryu was quite above Shikai Ichigo.
- Uryu's power in Lost Agent arc are mysterios.
- In the War arc during Ichigo vs Kirgi, Kirgi stated that Uryu's is stronger than him. At that time Ichigo was also stronger than Kirgi, i see that as Kubo's parallel for Uryu strength and his potential. It lead me to assumption that during this time Uryu was around equal to Ichigo. It don't sound like asspull to me, particularly when Ryuuken stated Uryu's potential way back in the Arrancar arc.