New users may search in vain for a log of all Filled Out Form events plus their point-in-time form data. (That is, even if field updates were blocked or values were later overwritten, you see the values that were on the form when each person clicked Submit).
First: it's not correct to say that Marketo doesn't store the original data from form posts: in fact, the REST Activity API includes historical POST payloads, including since-overwritten values. But it's true that it's not easy for a non-developer to see form data history across leads.
When seeking such a report outside of Marketo, users tend to say a “Google Sheet” (as opposed to XLS/CSV, Excel 365 online workbook, or something else). I'm not a Sheets user myself unless forced, but I know how it's done, and it's reeeeeally easy. So that's what we'll use today.