That is a case of yet another pair of problems, though: Python is incompatible with itself across versions (understandable, I guess), yet it is hard to run multiple versions side by side (major flaw in Python 3 for reusing the unadorned name Python, instead of making the number part of the name or changing the name of the installed software)
Python 3 does not reuse the unadorned name "python". It installs itself as "python3" by default. The decision to have "python" be Python 3 was solely Arch's.