It is not ONLY a cultural thing; intrigue and assassination has been almost a hobby in Seanchan from the very start, to an extent that makes Cairhien look like Andor or the Borderlands. That ter'angreal is invaluable; IIRC, part of each Empress' coronation involves all nobles assembling before it to swear loyalty. That would go a long way toward explaining why revolts are so rare in a country where minor nobles are EXPECTED to constantly plot their superiors assassination. Lesser nobles betray and murder greater ones daily, and every Empress loses multiple children to such plots even from their own siblings, then commends it as good strategy, but an assault on the Empress HERSELF (may she live forever) is unthinkable. The Crystal Throne is almost a certainly a big reason why, one that would not be lost on any member of the imperial household, let alone a sul'dam.

If Rand, does, in fact, pledge his allegiance to the Empress at any time, she will almost inevitably require it be done before the Crystal Throne itself. Coming from an Oathbreaker, she probably would not credit his pledge on any other basis.