Note that most terminal applications still use virtual terminals (`/dev/pty*`), and it is important to provide standard interface here.
Also, terminal makes it easier to debug failing UI, and host headless OS.
You forget that _all_ modern OS transcend the desktop: they support phones, tablets, and headless devices.
Despite what Haiku's sole full time developer says, Haiku is a FOSS recreation of BeOS, and BeOS was clearly and explicitly designed not to be another flavour of Unix.
If you feel that the OS world begins and ends with Unix, then we have nothing more to talk about. It's one data point on a vast and branching tree, and while it's shifted a lot of units, that doesn't make it especially significant or interesting.
In the wider space of graphical desktops, Unix is a poor, third-rate entrant. Anyone half serious about talking about OS development and implementation in general should be able to name half a dozen non-Unix OSes that do at least some things better in various ways.
Your points all assume that BeOS is trying to be a better Unix than Unix. It was not. It was not trying to be a Unix at all.