Give option to access workbooks open in an excel inatance into a single window like browsers allow multiple pages
Give users the option to use a single master window for all workbooks opened in an instance of excel. Display separate workbooks in subwindows.
This would eliminate the tedious swapping through every single open workbook when cycling through active apps.
Making it an option would satisfy power users who are deeply angry about the loss of that functionality, but allow the more casual users to retain their simplistic model.
I won't document all the many many many reasons that pretending that each open workbook is a separate process is damaging to productivity because that those details are cery readily available to anyone from Microsoft who might actually want to pay attention to their users. Or, you could continue to ignore this because you hate power users and only want to cater to the complaints of inexperienced novices.