Honestly, the automatic datetime conversion is the worst part if you're just trying to keep it text. It's idiotic there isn't a simple way to turn off that off. That's not formatting, that's actually changing the data in those cells which may not be what you want.
In case you're not aware, the latest version of Excel absolutely DOES have that setting (mentioned elsewhere here in the comments). While it's wild that it took so long, it's now a solvable problem and everyone should know about it (and upgrade)!