Echoing what was said above, practice. It’s normal to feel overwhelmed when taking on a new role. The “expectation” the game places on you to do good DPS at a high level is essentially that your rotation is a given, your resource (in your case, mana bars) management is pretty natural, and then your focus goes into fight mechanics.

I’m sure that sounds impossible right now, but it’s something that only gets better incrementally as you commit your DPS rotation/mechanics to memory and muscle memory. “Always be casting” is critically important and even subtle pauses between skills while you remember what to press add up to the biggest DPS losses.

Your post focused on the overwhelmingness of it all, so that’s the best answer I can give to that specifically. Of course, you should also take advantage of guides so that the rotations you’re committing to memory are the correct ones. After all this, when your damage is already solid, you can think about fight-specific optimizations. Places where your rotation might deviate from the norm due to add spawns, bosses jumping, etc. That stuff will push you into the upper echelons of damage, but the fundamentals come first.

Regarding parses, log comparison, “what is the definition of good damage,” and similar questions, use this information to your advantage but use it judiciously.

If you just got RDM to 70 and threw some middling gear on it, don’t be upset when you’re parsing “grey” on fights mostly being cleared by fully geared people. Look at the absolute number differences and, when you can, look at timelines and spells cast to make sure you’re executing properly. Someone with full gear landing Verholy for twice as much damage as your Verholy isn’t you making a mistake. It’s the nature of gear. But if the good players are casting their spells in a completely different order or at a much faster rate, those are things you can do something about.