1.) Spell Alert Animations. I remember having all the ui firing off when I used to play in Cata. The add-ons for spell alerts aren’t the same, and more add-ons means more UI bugs.
2.) I shouldn’t be getting killed by friendly guards when I exit a dungeon.
3.) Why do Zeppelins cause you to DC and spawn 40 miles away. I just traveled there and waited for it, it’s frustrating getting on it just to have to travel back and wait again.
The addon is actually better because it has a built in fade when the duration of your buff is getting low.
https://www.curseforge.com/wow/addons/spellactivationoverlay
Add in Supreme Defender WSG achievement not tracking
and the stormstrike animation is missing for enhancement shamans
Add the mount bugs and broken quests (especially Worgen).
The only time I’ve ever experienced this is on the boat to Vash’jir. Every single time I go there on a new toon, it disconnects me.
The Bug I want them to fix though, is the spell alerts. I’ve had to make do with custom Weakauras, which, like you said, aren’t as good. Hopefully Blizz fixes the bugs in this upcoming patch.
We’re also missing the multilayer map selector that was originally added in WotLK. In dungeons like Throne of the tides, if you’re at the first or second boss, you can’t see where a player that just joined is on the map.
From the 3.3.3 patch notes https://wowpedia.fandom.com/wiki/Patch_3.3.3#User_Interface
They’re also still using the WotLK Auction House, despite promising “An updated Auction House system arrives to provide a streamlined experience”. You can’t even search for relics unless you enter its exact name, because it still shows non-existent totems, idols, and librams under armor.
Thank for the information on the better than add-on.
And yes, I’ve noticed all of those bugs too especially the map one when in dungeons.
It’s crazy, because Cata was already there how did they make it worse? Lol idk what it takes but I imagine it’s very easy considering all of the hard building from scratch up was done.
I actually find this one to be funny. It seems to be any instanced content though, not just dungeons.
Anyone else notice that the Headless Horseman’s Mount doesn’t run right in the air anymore? It doesn’t gallop, it tiptoes.
Oof lol
It’s wild to me the number of original features that are just… not there, in Classic. Blizz is phoning it in HARD.
That is because they replaced it with a TN Walking Horse 
also there is a bug that wont let you link spells anymore when pressing shift … was useful for making macros now it just casts the spell your trying to link…very annoying
The guard killing is when you zone in to a neutral zone from a hearth or leaving a dungeon. The bug was reported before release and I have reported it at least 10 times between May and August and it’s still not fixed so I stopped reporting all bugs. They dont give a flying f about cata.
Also standing animation while riding the guild lion mount.
Warlock (and I assume hunter) pets are still despawning on Al’akir phase change, several bosses cause pets to glitch out and not attack.
Loot-A-Rang is still not working
Deathnight’s dragon skeleton flyer mount is still afraid of water.