> Python is by most measures the most popular language and became so AFTER that switch

The switch had nothing to do with Python's rise in popularity though, it was because of NumPy and later PyTorch being adopted by data scientist and later machine learning tasks that themselves became very popular. Python's popularity rose alongside those.

> There is no reason for anyone to be complaining about it being too hard to upgrade in 2026

The "complaints" are about unnecessary and pointless breakage, that was very difficult for many codebases to upgrade for years. That by now most of these codebases have been either abandoned, upgraded or decided to stick with Python2 until the end of time doesn't mean these pains didn't happen nor that the language's developers inflicting them to their users were a good idea because some largely unrelated external factors made the language popular several years later.

> that was very difficult for many codebases to upgrade for years.

In case people have forgotten: python 3.3 through 3.5 (and 3.6 I think) each had to reintroduce something that was removed to make the upgrade easier. Jumping from 2.7 to 3.3 (or higher depending on what you needed) was the recommended route because of this, it was less work than going to 3.0, 3.1, or 3.2