AdjustDateTimeStyleFormat: Don't adjust format when no conflicting options are present?

[anba]

AdjustDateTimeStyleFormat determines a new format even when no conflicting options are present. This leads to the following results:

js> console.log(new Date(0).toLocaleString("ja", {dateStyle: "full"}))                                                                           
1970年1月1日木曜日
js> console.log(new Temporal.PlainDate(1970, 1, 1).toLocaleString("ja", {dateStyle: "full"})) 
1970/1/1木曜日

The polyfill already appears to use the original format, because it returns:

> console.log(new Temporal.PlainDate(1970, 1, 1).toLocaleString("ja", {dateStyle: "full"}))
1970年1月1日木曜日