I disagree, I think the usage and meaning of 'alt' is in fact complicated. I've asked many other people this same question and they've all given different answers.

The core underlying theme is that 'alt' gets used as a pejorative towards your outgroup. Your descriptions of the right here are quite uncharitable, which is a strong signal of your biased thinking.

You also conveniently didn't answer my question about % of the right you'd classify as 'alt-right' and the % of the left that you'd classify as 'alt-left'. I suspect the reason you chose not to is because of that same bias. It would make clear that you use 'alt' as a pejorative selectively towards your outgroup.

This is about as needlessly hyperbolic as claiming that everyone on the left wants to see the US turn to socialism complete with "reeducation" camps for anyone right of center.

You lack perspective.