There's another point I need to make here about Shikai in general.
How common is it for shikai to be fully controllable upon the first release, because let's actually think about it. Between the shinigami's own reiatsu and self-control, the zanpakutou's spirit, and the shikai's own abilities can we actually say that Ichigo would be an odd one, aside from achieving Shikai in the Academy?
Canonically, Zangetsu's sole ability was to gather reiatsu on its cutting edge with each swing, so if that's still true here, could it be that the sword would sometimes have way too much reiatsu within its blade to be discharged safely and then sealed? Especially when proximity to the reiatsu generator that is Ichigo?
Edit:
I mean, normally, a shikai would be achieved when a shinigami is in a Division, and then would work on it until they are ready to try to gain a seated position. So in that case, it would be perfect sense why control of a shikai means one is ready to be a seated officer.
They just gloss over the awkward training period before that moment.