It's interesting because I don't think the series ever fully commits to explaining the practical, moment-to-moment influence. Sure, we get the big reveal and the final power-up, but the day-to-day stuff is murky. His Getsuga Tenshō always had that blue energy, which later gets the Quincy-style black and red overlay, but was that Quincy influence from the start, or did it just merge later? His raw power and regenerative ability feel more Hollow-dominant to me most of the time.
Sometimes I wonder if the Quincy side is more of a passive framework—the 'vessel' that held the Hollow and Shinigami powers together when they should have torn him apart. That would explain his abnormal endurance. The active manifestations, like absorbing reishi or the specific final form, only show up under extreme duress or with external triggers like Yhwach. It's less a constant shaping and more a latent blueprint that only gets activated when the plot needs a new tier of enemy.
Honestly, the fan wikis make it seem like a clean fusion, but rereading the fights, it feels messy and retrofitted, which isn't necessarily a bad thing. It gives his power a kind of unstable, patchwork quality that fits his character.