Looking for tips for damage and defense as I've hit a wall in T16s at level 90!

https://poe.ninja/pob/7791e here is my pob for anyone open to taking a look. This is the farthest I have ever taken a self created build and I don't want to give up on it, I'm really proud of it although I'm sure its probably terrible compared to many people out there. I've only been playing since last league. I noticed I am missing the mark when comparing my build to other people on poe ninja who are also using firestorm of meteors as their main skill. These people are hitting multi millions of damage in some cases and I cannot seem to crack even half a million. I have also since hit a wall in my defenses and find myself hard stuck at level 90, although I can clear T16s mobs relatively easy, I struggle at bosses and I'm getting one shot during them. But I managed to kill two of the uber bosses from the seasonal memory thread map mechanics! I am hoping the community can help me fill in some holes here whether that be through education on my defenses or maybe some obvious ways I'm missing damage. Thanks so much for anyone willing to take a look. It's been really satisfying for me playing this character and figuring out ways to become stronger throughout mapping!

You can try running maps with less aggressive and more predictable bosses.
For example Atoll map has boss totem that stands in place and the only scary thing it has is its ice nova that is very visually distinct.
Another way to stop getting oneshots is to roll out map modifiers you will struggle with. In your case your dont want to see spell suppression, extra enegry shield as life, more life, elemental resistances and enfeeble(figure out the rest yourself). This will boost your damage feel during mapping
For lowering oneshot count you'd also need to get rid of some modifiers, for example I get rid of poison and % of phys as extra chaos damage

this is best I can advice you with