Come again? Most people install the windowed version of it today, but its history is very definitely TUI-based. All of the features you mentioned are things that have been added along the way as its container was able to support them.
Historically being TUI-centric doesn’t mean that it is not GUI today, right?
It supports all your fonts, font ligatures, varying font sizes inside the same buffer, renders images inside your buffers, all without relying on a terminal emulator or Sixel support. Sounds fundamentally not TUI to me.