Correlation and causation always difficult to tease out here... For me, globalisation was deflationary - so long duration trades worked well. Deglobisation is inflationary, so short duration trades work well. That BOJ made money with a long duration trade does not mean that the BOJ strategy made JGBs a buy.
Sure Japan has large reserves relative to other countries, but with 9t (USD equiv) of gov debt, having 1t of reserves is not that sizeable.
Have you seen this one: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4620159
What about Japan?
Correlation and causation always difficult to tease out here... For me, globalisation was deflationary - so long duration trades worked well. Deglobisation is inflationary, so short duration trades work well. That BOJ made money with a long duration trade does not mean that the BOJ strategy made JGBs a buy.