Thanks but... yuck. Any way I can remap these?

Cmd-<number> is a pretty standard way to jump to tabs (and arguably, Ctrl-tab as well).

⌃⇥ actually does work in Terminal.app. And in fact, ⌃⇥ and ⌃⇧⇥ are the official keyboard shortcuts in the menu, with ⌘{ and ⌘} being undocumented aliases. This is also how Safari works too.

I wonder why they chose ⌘{ and ⌘} instead of ⌘[ and ⌘]. With the later you don't need to hold down SHIFT (at least on US keyboard layout.)

Because it's the same keyboard shortcuts that Safari uses, and in Safari ⌘[ and ⌘] navigate the history stack.