Converting Google sheets to Excel 2003 (.xls) using Apps Script

Currently, it seems Google has no way of converting Sheets to .xls format. So, I'm trying to use App Script to parse values from Sheet into a .XLS format. Here's the sample code below.

var sheet = SpreadsheetApp.openById('1...3f');
var sourceFolder = DriveApp.getFolderById('17..f');
sourceFolder.createFile("Test File",sheet.getSheets()[0].getDataRange().getDisplayValues(), MimeType.MICROSOFT_EXCEL_LEGACY);

Data in Sheets has headers looks like this: sample data

However after converted to .xls, it looks like this all in cell A1: Name,Age,Fred,30,Jane,25

I've tried using:

Drive.Files.get(fileId).exportLinks[MimeType.MICROSOFT_EXCEL_LEGACY]

But Google doesn't support it. Has to be MimeType.MICROSOFT_EXCEL. Any help will be appreciated.