A place in the World Test Championship final is in place. So this series was much more important then Ashes. Would you rather win the first WTC or Ashes.
WTC is going to be equivalent to ODI World Cup or more.
I do agree sometimes the rotation does seem less than perfect but with Covid and the sheer amount of cricket in the next 12 months I can't see they have any options other than to rotate players,mainly the bowlers...
Players like Anderson and probably broad don't want to be rotated but they are towards the end of their careers and so far have been pretty much injury free. Anderson is 38 and if he does get an Ashes place it would be remarkable testament to his physical fitness and maybe......down to rotation thru this year. Similar with Wood who has been injury prone and seems to be getting less so in the last 12 months.
The WTC is nowhere near as important as an ODI trophy or an Ashes away win. They are both rare but I've been supporting England since about 1980 and I didn't think we would win the WC in my lifetime