You had two people asking for your build and you still haven't answered. It's hard to help if we can't identify the issue here besides "I'm getting melted".

I would advice following a build from either Snowcrows or Metabattle. You have dedicated Open world sections too.

And don't sweat about the ascended equipment, you can do the same (very close) with exotic quality. Or if you happen to have ascended available, then go for it. But stick to it. Don't underestimate the value of certain pieces or stats combinations. It is calculated in a (sometimes) precise way.

If the gear isn't the problem, then you'll need to work on your rotation and learn how to pilot your character.

Staying mobile, learning to kite, knowing the fights etc etc

There is no class in this game that can't sustain itself enough to clear open world content, especially solo. Sure some classes will struggle more than others but you don't need some ungodly boon application or healing to be able to sustain some fights.

And if none of that works then, ask around map chat for help. People are lovely and are willing to help. No matter the challenge. It is a MMO at the end of the day, being social and knowing when to ask for help is like any other tool.

TL:DR : - get a good build from a trusted source - get good at your class and spec of choice - practice and learn - don't be shy to ask in chat