It's not about commutativity, it's about possible error states. What if, after directly typing `<`, typing `=` does the right thing, but then when you backspace, the resulting node correctly outputs LaTeX of `<` but its state is messed up someotherhow such that typing `=` again won't work?

`assertFullyFunctioningInequality()` checks not only that the inequality has the right LaTeX and when you backspace it has the right LaTeX, but also that when you backspace you get the right state such that you can either type `=` again to get the non-strict inequality again, or backspace again and it'll delete correctly.