You may think that's pedantic but it really isn't. Half-decent TUIs are much closer to GUIs than they are to CLIs because they're interactive and don't suffer from discoverability issues like most CLIs do. The only similarity they have with CLIs is that they both run in a terminal emulator.

"htop" is a TUI, "ps" is a CLI. They can both accomplish most of the same things but the user experience is completely different. With htop you're clicking on columns to sort the live-updating process list, while with "ps" you're reading the manual pages to find the right flags to sort the columns, wrapping it in a "watch" command to get it to update periodically, and piping into "head" to get the top N results (or looking for a ps flag to do the same).