It's possible to change the stats of ascended gear. Exotics are different but they are much easier to acquire.
It's not so simple.Optimizing your DPS often ends up just being a matter of pressing buttons when they come off cooldown with no other nuance. The most complicated professions in the game are merely the ones with the longest sequence of inputs in their rotation. There's no concept of procs or synergies or resource management
https://wiki.guildwars2.com/wiki/Combo
The Engineer rotation is really complex which is why I choose a much simpler one that does around 90%-95% of the DPS. There are some simpler rotations but that almost always comes at a DPS loss. Then there are things like dodges becoming part of your rotation for thiefs. GW2 can be very easy to play but if you want to max things out then you will end up with a more complex rotation. I'm pretty sure that goes for most MMO's.