Archnemesis said:
He wasn't top of his class, but he was near it. Keigo got upset because Ichigo wasnt in the low ranks like him, which surprised him because Ichigo barely paid attention even before becoming a shinigami and being distracted with saving lives and whatnot. Pretty sure Ishida was top of the class, they show it in the episode he's introduced. Isshin never rode his ass, he even states he has a hands-off approach to parenting (but not with the girls lol). I think the school grades bit shows that he can understand things without really trying, so if he did focus and put his mind to it, he could easily.
Without a doubt his intelligence is nowhere NEAR the people you mentioned - Ishida, Urahara, Aizen etc. But hes smarter (intelligent....er) than the average bear.
Also, to me it seemed he was able to control his spiritual energy in that cannon ball, it was just too much for him to be able to lower the amount of power. (sorry for ref another manga) but it's kinda like Soul Eater, where blackstar's wavelength was too much for the other two - it's too big for him to control with such finesse. But i do agree that he lacks reiatsu control in general.
Lacked, is the word.
After jinzen his reiatsu control was good enough to sense others from few miles away(which he did again with rukai and renji and byakuya previous chapter).
Not to mention that the whole fullbring thing is all about control.
I'd say that Ichigo does have similar intelligence capabilities to those mentioned character. What he lacks compared to them is knowledge, but when he puts his mind to it he can surpass others quite easily and is quite good and strategizing as well as predicting people.
So if he needed to, he could be able to put together his version of quincy blut techniques - after all he learns best in intense stressful situations.
Deicide as well as fullbring arc clearly parallels Ichigo to Aizen - Ichigo is basically "Aizen's beginning"