It seems you are both saying the same thing. Had Python not introduced a line in the sand and instead continued to support Python 2 amid future updates there would have been no reason for Python 3. The Python 2 line could have kept improving instead.

Just as you say, Python could have introduced what is found in Python 3 without breaking Python 2 support. Which is the direction Go has settled on; hence why Go 2 is off the table. Go 1.0 and Go 1.23 are very different languages, but backwards version support is retained, so no need for a new major version.