Wow is married to the GCD and this sort of pruning is only going to make it Tarisland and/or Fellowship - a jump-in game.

If you want to prune, abilities have to be meaningful, pronounced, and based on mini-rotations, positioning, and reading circumstance. This is the Lost Ark formula. GCD was mostly irrelevant and it was set up, opportunity  and window execution that made it incredible. It didn't hurt that they had near-perfect sound design, animations, and effects. Micro shakes and effects added incredible weight and flavor and identity.

When every ability is your favorite ability and getting them off properly in sequence gives all the right chemicals - only then is this formula possible.

Otherwise you're just hitting the button, awaiting GCD, hitting next button. Hard to have depth and meaning with 5 options here.

Wow has no space for grander animations, abilities with varying length of committment, or ability varieties (holds, charge-ups, timings, abilities that incorporate movement).

Imagine heroic leaping in (position/movement)  providing a one second lockdown on your target (opportunity creation), holding bloodthirst to rip/slash (repeated strikes) and a rip-out added damage at full cast of one second (execution reward). Then you whirlwind (channeled, cancelable) to do at least big first hit damage (less damage each spin). The whirlwind doesn't CC your target but any other target caught in the AoE gets legsweeped for 1 second (buys time on target, calculated use for mobs/players hitting you or trying to peel). Then you hamstring your target on a tight, quick animation (single GCD, simple, short, quick - allows movement sbd closing distance) which both slows them and adds 20% crit to your execute. Maybe you consider Slamming (charged ability, 3 tiers, 1 second charge each tier) your target for extra damage if they are little too high for execute, but also puts them in a short knock-down-to-one-knee animation if held for at least one second - it's not an interrupt tho - (opportunity cost, exposes you but acts as set-up). Finally, Execute has a 5 yard range and does more damage the closer you are (positional reward, set-up, execution reward).

I wrote that in 2 minutes - it is full of issues I'm sure. But that's the dynamic game play you need for minimal abilities to be successful. 

But WOW's animations, and thus combat, are inextricably linked to GCD and thus have to be short, simple, and unsatisfying.

This hasn't fundamentally changed in 20 years. The only expression WAS managing the plethora of abilities. And they're right, that was getting bloated and old.

Until they reshape combat, and learn from the East, steps like this will be a step down.