Google-sheets – Remove the false operator in Google Sheets

Cells containing the empty string "" appear empty but are not (isblank returns FALSE for them). They get sorted ahead of nonempty strings, which is not what you want. To avoid this, replace

if(isblank(B1:B), "", datevalue(B1:B))

by the simpler

iferror(datevalue(B1:B))

The command iferror returns its (optional) second argument if there is an error evaluating the first argument; otherwise it leaves the cell blank. Blank cells are sorted to the bottom.

A potential drawback of the above is that misformatted dates are simply ignored, while you may want to see and fix them. This is something you can address separately; e.g., have a column with

if(isblank(B1:B), 0, if(iserror(datevalue(B1:B), 1, 0))

and sum over it to get the total number of nonempty but invalid date cells.

Another potential issue is that you are sorting a range containing arrayformula. The sort may move the formula to another row, creating a mess. It's safer to exclude the header row from sorting. Replacing

var data = JobList.getDataRange();

by

var data = JobList.getDataRange().offset(1,0);

would do it.

=AVERAGEIF(A1:Z1,"<>")

"<>" on its own means "not equal to an empty string" in Google Sheets.