In Premiere I do the sequences in PAL widescreen and they scale to frame size. (White part a little larger, otherwise black borders)

Edit to the end with original sequence settings, only then will the 1440s s.Encore given or Resolutionexportiert as file in SD.
That it pixelt at hochskaliertem material is surely clear?

The same material but not in pixelt mpeg mov ausgerendert but not!
And that's why I wonder, yes!