Just to dismiss the idea that bank staff are disappearing, I see this:
Currently banks employ 25,000 people.
In 1980, they employed a touch over 10,000, so 2.5 times more now.
The population of NZ has increased by about 1.8 times in that period.
So, despite the massive investment in automation, they still employ more people.
End of that story.
Nope, it isn't the end by a long shot. I'm calling BS on your 10,000 figure in 1980.
In 1980, there were at least seven registered, nationwide and "trading" banks in New Zealand - POSB, ANZ, BNZ, National, BNSW, CountryWide & ASB. There were also 12 regional banks that took a common name of 'Trustee Banks' in 1984 - and changed their names to reflect this. They became known as "TrustBank (region name)".
In 1980, the ANZ alone employed 2,806 staff in NZ
Warning: 6.75 MB PDF -https://www.anz.com/content/dam/anzcom/shareholder/1980AnnualReport.pdf
In 1980, the BNZ had 321 branches employing 455 managerial staff alone, and over 2500 other staff (total 2955)
Warning: 7.69 MB PDF - https://www.bnzheritage.co.nz/assets/Uploads/Annual-Report-1980-reduced.pdf
That is just two of the 19 banks, over 5700 staff (more than half your BS 10,000 figure), and they were not even the biggest banks in NZ at that time (which was the National Bank, with over 700 branches, more than twice the size of the ANZ)
Based on just these two, realistically, the 1980 figure is more likely to be over 23,000.
Since you introduced population, I'll take the liberty of doing that too. The NZ population in 1980 was 3.1 million, by 2013 it was 4.4 million, and now its almost 4.9 million (by the way, that's 1.6x not 1.8x)
So, if we take the more realistic 23,000 in 1980 then the staffing now, in 2021, should be more like 34,150 - a figure that ties closely with the actual figure in 2013, when banking and finance industries in New Zealand employed 35,793 staff and managers.
Warning: 11.18 MB PDF -https://www.productivity.govt.nz/assets/Documents/bcea812a17/New-jobs-old-jobs-Working-paper.pdf
The fact is that if, as you claim, bank staff levels are unaffected by, say automation, then there should be over 34,150 bank staff in NZ. You say there are 25,000, so that is a estimated nearly 10,000 (27%) reduction, and a definite over 10,000 (31%) reduction since 2013!!
My researched, actual facts trump your BS guesswork!