I think you're not entirely wrong, but the big question is also: Why tie in additional character progression systems?
Imagine for a moment, you'd log into Shadowlands, choose your covenant, get your "borrowed abilities" and that's it, no need to grind Renown for Soulbinds, no need to upgrade conduits, no upgradeable legendaries, the sole character progression you have from that point is getting better gear.
Receiving an ability but knowing you'll quite likely lose them doesn't feel amazing, but what in my opinion absolutely spoils the deal is Blizzard attempting to tie in additional character progression into those systems.
Previously, your entire character progression past levelcap was gear based, when a new expansion came out, you received better gear, you replaced your previous expansion gear "organically" in some way, because the newer expansion gear was just plain better.
With those new systems however, Blizzard comes in and just disables them, you didn't replace your Legion Artifact in BfA because some green weapon was "better", but because Blizzard went in and disabled bonuses accumulated over an entire expansion.
With those abilities, you can at least integrate them into a talent or make them possibly baseline with some tweaks with the next expansion, but it's a certainty that all that "additional" progression accumulated over the course of an expansion will land in the trash.
Giving a set of expansion specific abilities is not necessarily bad i think, but those alternate power progression systems that will be irrelevant the second the next expansion hits, need to go.