While I see what you are saying about comparing a longer time range to a shorter time range, I am not sure what outcome you expect when trying to look at a Daily granularity?
If you are comparing 30 days to 15 days in a grid, the 15 days range can only ever show 15 rows of data, whereas the table as a whole will show all 30 rows...
The table isn't really showing you content outside of the range, those days (that aren't in your range) technically are labelled, but they will always show 0 because they are outside of the range. You could raise this with client care, but I assume a small visual issue like this isn't going to be high on the list to fix. It's the same as if I create a segment that says "pages that contain section" then I have two columns, one where my segment is stacked with a metric... I will still see pages that aren't sections, because my other column still has relevant data...
You can always set the column settings to "Interpret 0 as no value"... while you will still see the "dates" display, the rows will be a little cleaner:

Comparing different ranges will always have challenges. This is a minor display annoyance, but shouldn't impact your data or comparisons in any way.