I do get your point - but using a tool like Make makes this type of activity much more approachable for most people. (Most Knack users won’t know what cURL is).
With the Mailhook approach, you can in principle send any data in the body of the email - but I find it simpler to just trigger with a record ID and then retrieve the data. This also give you the opportunity to access data that is not available in Knacks email (and presumably your concept) process. In a scenario you can retrieve data from multiple objects (and update them of course). I think, personally that Knack / Make is a pretty unbeatable combination!