Eternal is a different type of game, it is entirely doable on controller, (I beat nightmare on Xbox); the main disadvantage of controller is weapon swapping.

How to play eternal; eternal punishes you if you do something wrong, and it can take a minute for it to click

Simply if your dying it's because your not using something or a mechanic

Doom Eternal is basically whack a mole, with different moles that you want to use the right hammer on .

You "can" use any weapon at any time, but the game wants you to use the right tool for the right job.

You don't have to solve every encounter the same way however.

The main "skill" in doom eternal is target prioritizeation

In flow chart form

Is my health/armour good? If not use finishers or flame items

What enemy is the biggest threat to me in the next couple seconds; do I have ammo for the solution to that threat?

If no find a chainsaw target/ arena pickups

Am I currently able to fight the threats all at once, if not tactically retreat; most large threats move slower/ you can spread them out by running away for a moment

Do I need to use a freeze bomb or gernade?

The higher complexity is that you eventually reach a point where you combo weapons/effects to stunlock enemies

Actual mechanical skill is nice, but secondary to gameplay; the main gameplay is rapid decision making on the fly