Head on, they do not build up for a strong system.
Don’t get me wrong, inside every Covenant the theme pulses perfectly. Every Covenant has a strong flavor, has a strong visual and ambience theme – but together they do not form anything whole, they are simply not parts of a single realm. Whatever approach you take.
If we split them by role in Shadowlands, it makes no sense. Ok, Maldraxxus are defenders of all Shadowlands, and Kyrian deliver souls as ferrymen/women, but the other two… do nothing for the whole Death realm. Besides, while Kyrian indeed ferry souls for everybody, you cannot explain the presence of local military in every Covenant, given that Maldraxxi are supposed to take care of threats – all threats. In Agthia’s Repose, Kyrian fought the void invaders. If Maldraxxi are the defenders, they should have had garrisons in all Covenants, and serve as a police/army for the whole realm. Who you’re gonna call?
If we split them by virtues/sins, ok: Kyrian is self-sacrifice, Maldraxxi are valor, Venthyr get redeemable sinners, but Ardenweald… Nature-bound souls? Hello, but Nature is not a character trait, it’s, well, a hobby. Besides, valor and sacrifice walk hand in hand – no wonder that Mograine is confused and questions Arbiter’s choice for himself.
If we split them by visuals, Kyrian, Fae and Venthyr would totally answer their theme, but Necrolords?.. No. Not in one culture death and decay, skeletons and rot, would be seen as a nation of proud warriors. It’s the mere nature of decaying body not to be something solid, robust and full of virtues.
Whatever approach you take, one or more Covenants would fall out of the system. No wonder that many players, including myself, are struggling to find their spot in afterlife, presuming they died in Azeroth. You get one of five choices: self-sacrifice and oblivion, Valhalla combat, endless groves (with ants crawling into your pants), torturing others (so called “atonement”) or rotting in hell. Sorry sir, but I see none of these options fit for myself, and I hardly qualify to any of these afterlives :)
Yes, there are supposed to be other Covenants, but presumably intended for worlds with Blue/Orange moral scale, not Black/White.
No strong system, and it sucks. If we try to build an analogy, current Covenants would be like: bread, bagel, milk, chalk. One or two would always be from another deck of cards – whatever is your point of view.