User blog comment:Silver-Haired Seireitou/Revisiting Hakuda/@comment-1493741-20150516093556/@comment-1493741-20150516164543

Its a little weird to disregard "Hollow Reiryoku" and "Fire-elemental Reiryoku" when Cero isn't stated to be a Reiatsu-based technique either, in the manga (Now, now, before we get into anything, yes, Hierro and Bala are, but Cero is not exclusive to Arrancar, the latter two are). His Shinigami powers being born from the weird shit Isshin got into with White would just as well explain why his abilities feel similar to that of an Arrancar. On top of that, the fact that Ichigo has no control over his own Reiatsu, tanking a hit to the face (Or pimp gripping it) could just as well be the only means of gauging his relative power at that stage. But none of that was what I asked about.

So, on that note, I get where you're coming from and it makes sense, its not what I personally subscribe to but I'm not going to discount it out of hand. After all, either way could work. The way I see it is just that Reiryoku is "internal energy", its used to fuel abilities and is then cast out in any given form (Spells, techniques, what have you) while Reiatsu serves as "external energy" and is harder to work with without a physical form, thus its typically exuded as just pressure (Or an elemental form as aligned with their wielder) but can be molded and shaped (Hierro, Bala) with training and so on.

Thanks for the explanation, Sei.