There was a shift years back, you can download the old legacy workout files still from here:
This does not however fix your real request of planning.
I would suspect this… will never be “fixed” or ever become a feature unfortunately, believe it’s been probably the top request/complaint since the change and planning feature added in companion.
As broken of an alternative I can think of; an ugly but technically functional solution would be to use something like Intervals.icu and upload the workouts to those days and have intervals sync with zwift.