> Just judging from what I read iso8601 is based off of rfc3339 (as i assume the "request for comments" phase is before the iso standardization).

No that's not how this works. The ISO one is from the 80s, the IETF one from the 2000s. It's the other way around. The RFC is a profile of the ISO.

> ISO slightly improved the rfc, but it is largely the same.

This is not a true statement.

> ISO has taken the free (as in speech) and is now selling a derivative work.

This is also not a true statement.