Type inference in excel has wasted countless hours of my time
No, no it hasn't.
trying to make sense of corruption caused by third parties using excel.
So close and yet so far: your own comment explains that it was caused by third parties using excel... badly.
I do fault excel itself because these errors are pervasive.
No, it's because you're ignorant. Every spreadsheet has exactly the same problem. They are designed to work on numbers, first and foremost. If you want to work on text in them, you have to take additional steps.
They could have better structured the data imports or made them less creative or asked users for more feedback or have the import do a pass over the entire datasets checking for outliers that may suggest a different type.
They could have, but then they could have easily got it wrong and made people angry in that way. Instead, they are being consistent, and always doing it the same way.
When a critical mass is "doing it wrong" becomes pointless and counterproductive in the real world to continue to point fingers at users. Tools are supposed to be useful
Spreadsheets are very useful for doing the job they are meant to do. The problem here is users doing something stupid with a spreadsheet. They should be using a database. You can whip up a web database with CSV import and export from a CMS in a few minutes' time just by clicking. It will enforce data types and it won't mangle anything. They're not even doing spreadsheet-type manipulations, so there is no value to using a spreadsheet. You don't redesign screwdriver handles because some people are using them as hammers.