I've mained a Mag DK since 2016, at one point about 2 years ago I had like 6 different MagDK's and I played every one of them differently in PvP. The class was so versatile, I barely played other classes....
-- I don't know exactly why the game evolved in this direction, but it went like this. The Psijic Skillline came out, and every PvP group in Cyrodil was running Timestop, people complained and I guess the answer was to add ever increasing immunities to everything.. to the point where MagDk barely has a purpose.

We can DragonLeap or we can throw out a Standard and some AOE's, but most would rather probably have a Sorc with Negate, and Negate even does more damage- so the class has become an afterthought.

All of identifying skills have been decimated by the 'Perma-Immunities we now see in PvP'

TALONS- There are players that now easily have a permanent immobilization immunity, or if you do get 1 talon they instantly break it and get the immunity timer. Even prior to the constant Immobilization Immunities you had to use more than 1 to be effective. You had to spam 3 or 4 of these to keep a guy in place or in Cyrodil try to hold a doorway.
FOSSILIZE- This skill is worthless. It' will be darked out for entire 30 minute battles
THE CHAIN - Another Skill that is useless when your opponents always have movement immunities
CINDER STORM This at least had a use with it's 70% snare, I might be mistaken, but didn't the game recently add ways to ignore snares also?

What about our DPS
WHIP Yes, our primary DPS... first you added a Timer to the already slowest primary attack in the game just to make sure we couldn't build around it and ever do two or three in a row (which was probably the most fun this class ever was btw, and it was far from OP), but now there more immunities to off balance also...
DLEAP still a very effective Ult, but the stun was such a big part of this, now you rarely get that follow up attack at all.

The entire identity of Mag DK at one point was controlling the battlefield, most of our skills were built for this, and it isn't even in the game anymore.
Every update there are more ways added to make sure players can avoid getting stunned, immobilized, snared to the point where most people I play with don't even keep any skills on there bar for this purpose... you try to quick combo kill your opponent or bomb build because anything that involved more than 10 seconds of combat will involve the other guy kiting around rocks or a tower or something.

Aside from really making this class exceptionally one dimensional and dull the entire PvP direction has digressed toward a 1 dimensional build style. I would argue Cyrodil was a better experience when an organized group of 10 defenders could utilize different classes, seige equipment, and hold off sometimes 30 or 40 attackers with immobilizes, oil, tanks, healers, etc----
it was far more strategic compared to the version we have now where tight little ball groups all spamming the same 2 or 3 skills and Ults mindless just run around until another group of exactly the same build more or less stops them by blowing them up first.