There’s no room for specifics in a forum reply but I can give a small example.
Resto druids have efflorescence, MW has jadefire stomp.  Both are ‘maintenance’ healing spells needed to setup healing.  Efflo stacks mastery and stomp is crucial for all fistweaving.  Both are positional and need the player to pay attention to fight mechanics, positioning, tank movement, etc (all good things IMO)…
Efflo has no cooldown, instead it’s mana and GCD cost make it sub optimal to spam, but can be repositioned if needed.  Stomp has a 15s CD, mana cost, GCD cost, and a talent that causes it to ‘have a chance’ to reset.
Efllo requires no special UI consideration.  No WA to track, no bars, no buffs (they do exist, you just don’t need to pay attention to it).  You look at the game, the players, the fight.  Are people standing in it, win!  They aren’t and I have a free GCD, recast.  All the information I need to make a decision to cast or not is in game, not in the UI or buffs.
Stomp requires tracking.  Either through a WA, or something.  Not only does it have a CD but it also has a semi-random proc to reset it’s cooldown.  It also interacts with multiple buffs all of which ALSO need WAs to track.
Efflo is good design, Stomp is bad.  Efflo requires the player to play the game, Stomp players are playing the UI.
The thing is, the problem isn’t the WA trackers, the problem is Stomp is just badly designed and so NEEDS WA trackers.  Fix stomp, and any WAs tracking stomp will disappear, no need to ban addons.
IF blizz actually was trying to fix the ‘complexity problem’, they’d fix it first and leave addons in-tact, since they are the perfect litmus test for their success/failure.  They are destroying addons, the whole bit about ‘to make the game easier/more approachable/less complex/less filling/better tasting/etc…’ is just PR platitudes.