IIRC correctly, an Adjuchas class Arrancar is already far stronger than a VL. Of course it is weaker than an VL class Arrancar.
Basically, while Fullbringers were infected by Hollows (Vizard's boundary was simply broken), Ichigo have likely been infected by this Hollowified Hollow - Incomplete Arrancar, which means that this hollow already had traits of both, Shinigami and Hollow. It explains why Ichigo was the only one that could use a Hollow Mask in Bankai and as well why his complete hollow, H2Ichigo, is not only compatible, but capable of even better utilizing a Zanpakutou, than it's original owner.
The instability of the hollow-arrancar that infected Ichigo, was quite likely the reason why Ichigo could revert back from complete Hollow with a Zanpakutou, to his previous state, a Shinigami with Hollow powers. It is instable, thus it could stand one foot at Shinigami or Hollow side, while the other one remaining on the line.
Of course there is still FGT, that incorporates every mastered power of Ichigo (you can notice it was incomplete at the fight against Aizen, because there were still some powers that Ichigo haven't touched upon), that actually allows to fully and perhaps perfectly utilize all of which made is Ichigo.