the leaders have one fixed agenda and two random agendas, they have no personality beyond that
I'm at the forefront of complaining that the AI has no personality in Civ VI, but what I mean by that is that a given civ/leader has no predictable pattern of behaviour between games, not that all civs necessarily behave identically at all times (agendas don't really count - AIs can complain about the same thing game after game without that actually affecting how they play).
There is some randomisation of personality traits such as aggression, Wonder-hoarding, victory preference, religious focus and so forth which has no relation to agendas (even if a civ has a wonder-hoarding agenda, for instance, it's no more likely to build wonders than any other). The problem is that any civ seems to have a roughly equal probability to display any of these traits (in the game I've just started I've been rushed by a horde of Australian warriors, for instance).
As Infixo says, there is a set of variables in the code which are supposed to modify the chances that a civ will exhibit some of these traits (so, for instance, Qin ought to focus on Wonders more than Shaka). As far as my experience suggests, these are however not expressed during gameplay - I expect the strength of the modifiers is too low in all but the most extreme cases (such as minimum aggression for Gandhi and Poundmaker, who will never declare war without being asked to) to result in reliable personalities being expressed.
In short, the game coding suggests that personalities are intended to exist, but for whatever reason in practice they don't.