started with potential and MC that needed to work hard to grow and even his growth was the route of Taijutsu however it seems like the writer had no motivation to go through this and just tossed it aside and gave the MC a cheat/Otsutsuki and a couple of years to surpass everyone, he had ideas but never went through with them,
Lazy writing
not bad but having read the manga which the creator of this did not fully delve into there are a lot of issues, Yumichika for example was confirm in FKT to be bellow Vice Captain level Reaitsu by Izuru/Hisagi, Ikkaku is also inferior to Grade 5/VC level from Ichigo fight and Urahara Statement of ichigo power during their fight as 4th Seat to Max 3rd seat and Renji in Base was already superior to Ikkaku in Shikai as seen in ichigo fight.
The Worst of all is the writer issue with Bleach Reaitsu Grading system, we know from Shunsui direct statement that the bottom of bottom Shinigami have Grade 20 but here apparently Grade 20 is ordinary person level. a Menos Grande using Ichigo as scaling should be around Grade 7/8 Reaitsu since Ichigo Post Shikai/Urahara training was confirm as Grade 6/3rd Seat.
as for the MC being Captain level as just a Gillian this is fine because Aaroniero was also a Gillian and reach baseline Captain in his Resurrection but in his case he was also an Arrancar.
other than this its actually a pretty decent FF using Bleach world which is extremely rare.