I looked at a few of them, and they seem to just be wrappers. How would I for example append a row to an existing Google spreadsheet? And how would I do the same with Excel?

Add a worksheet tablerow with Microsoft Excel API - https://pipedream.com/apps/microsoft-excel/actions/add-a-wor...

Add row to Google sheet - https://pipedream.com/apps/google-sheets/actions/add-single-...

I think pipedream is great, I have yet to figure out tge perfect niche for it though.

What are your ideal customers?