New castbar feature - good potential, but misplaced

Hi there!
The new castbar showing up on bosses is an interesting thing that the devs recently introduced, however i feel like it is both exectuted poorly and is much more needed in different parts of the game.

First issue: Boss sizes
There are many bosses that are incredibly tall and since the castbar shows around its head, it is a very common occurance that it is just out of screen and basicly does not help anyone.

Second issue: Why not add this feature to normal mobs?
This ties to a different problem - limited size enemy list.
Lets set the scenario - suppose im running Eureka Orthos and fighting mobs in aoe. All of them have some dangerous aoes that have delayed telegraphs. I think to myself "I pulled 10 mobs, i can see all their castbars in aggro list, im fine". However by mistake i have pulled 11 mobs instead of 10 and the last mob, that is out of aggro list, kills me with a mechanic because i dont receive the information about the attack.
Now imagine all of those mobs show the castbar above their heads - now i can play to the best of my abilities without being hindered by bad UI.
And even more, this would allow players to play better in regular dungeons, having more control with stuns and interrupts.

Bigger limit on aggro list would also be pretty nice, but its not the topic

It is a great feature. They need to add cast spells to it as well as cast abilities, so if something is casting a spell I can Interject or Head Shot, I can see it just as clearly as the abilities.