ever since the original Path of the Titans system was scrapped Blizzard have been looking to work additional systems into the game. maybe it's because of the disapointment at the scrapping of Path or the complaints about simplification of talents but Blizz seem convinced that expansions need to offer some unique system, some Big New to attract/maintain subscribers. Legion artifacts had their downsides but were hugely popular and, for the most part, worked quite well. BFA though... well it's a wonder they still stuck with it after that mess (don't get me wrong, I liked the expansion overall but there's a reason the Special System was overhauled each major patch and it's called "massive critical backlash")
the Covenants in Shadowlands seem like an experiment to have the Special Big New be something that's still central to the story and theme but with more optional components, which may be a step in the right direction. though of course there's no such thing as "optional" for many players (and there are good arguments why some things don't quite count as optional, especially for min/maxers) and it would be nice to have an expansion that can stand up without some new system for us to have to learn and then forget about when the next expansion comes along
that being said, I do like some of the new stuff. Renown seems like an excellent alternative to rep grinds (could possibly be worked into a new kind of rep system in future expansions with different factions having separate renown levels) and while Torghast does get repetitive after a while it still offers some fun with stacking different buffs and allowing us to become crazily powerful without unbalancing the game