Mana Generation
On a mana reliant tank, I shouldn't be getting 1/5th of the mana I used to get from Syphon Strike, and I definitely shouldn't have to worry about when my 60 second cooldown is going to be back up to then time it into my GCDs so I can keep going through my combo and still get that tripled mana from Syphon Strike. This is at least BEARABLE compared to the awful AoE mana generation (Oh wait, it's gone). It seems almost pointless to even put Stalwart Soul into the game because while yes, it's giving you blood and mana, it only gives you mana back as long as you deal damage to one enemy rather than giving you mana back per hit, like Quietus was after it gained the effect in Stormblood. On top of all this, Blood Price, another great mana generator is just removed from the game, and Delirium is thrown out the window as well and all that's left is a sad imitation of IR without the direct hit guarantee and a tiny 200 MP generation on hit, which mind you is only giving you 1200 mana (considering you land 5 Bloodspillers in that time). But while doing this, you've now wasted all of those precious globals on 1200 mana when you could have just been using them on your 123 combo. And with the removal of BW duration extension, it's even more useless of an ability.

Carve and Split is the only ability in the mana department that was reasonably balanced.

Overactive Inactivity
Playing Dark Knight feels like I'm putting in way too much work just to function as a job (ironic since that was the #1 complaint back in Stormblood), and every action I take on DRK seems like a fraction of what other tanks can do. You are now working three times as hard to do half of what you could in Stormblood, and after you've used up your only decent cooldown, you're stuck with the same mind-numbing 123 combo. It feels like I could be doing so much more, but since my entire kit is hidden behind a 3000MP wall or a 60 second cooldown wall, I'm stuck doing nothing in that time.

Something is clearly wrong with DRK, and I believe anyone defending its current state must have just went and unlocked it when the Shadowbringers trailer came out and dropped it at 70 until release.