im sure there are great psyker builds etc. etc. but this was also my experience partly.

i didn't die too often since i kited, used DoTs and knockdowns etc. however, as you said, once you are in yellow heat from 2-3 buffs you basically have to fight the enemy and dodge 2-3 anomalies or fight daemons at the same time. and to top it all off, you basically play 90% of the game with the purple hazy screen effect on.

it was not an enjoyable experience and i switched off the class around level 28. 

I think u have bin mit enough time to evolve. Psyker has strong synergies but it comes from skills and Armour and These armours drops Firsttime at lvl 39 or 40 the relics or archeo so run on normal till u have the first relics and give ur strongest ability shield for DMG which u must learn  from the skilltree and then Go slowly to + 1 or 3 but it gives u nothing when u do thus the First ancient i get was with 50 with a perk for +4 enemys to kill and use ur weapon when u get overheat.

Dots are to weak this Session u must have definitly aoe DMG 

You can turn the purple hazy effect off in the game settings.

If you don't want to die, you need some kind of healing on your character. This is true for all classes, not just the Psyker. Most common way is to use the Blood Balm innoculator component, which lasts for 20 seconds and heals 20% HP every second. It can easily carry you through the whole game. You can setup your innoculator components at Metrodora Thelema on your command bridge. It says Innoculator over her head.

Another common way is to get some HP regeneration or HP per hit effects.

HP per hit can be found on literally ANY item (primary enchant on weapons and belt items, secondary enchant on everything else).

HP regeneration (primary enchant) is limited to belt item, innoculator, neural implant and purity seals.

Other ways of sustaining yourself include using Void Shield, Precognition Psyker ability, Life Drain, Shield Drain, HP on kill, Shield on kill, Perks that give HP regeneration, passives that give HP regeneration and special relic-only enchantments.

Lol. Very true. But very true for all Classes really. In the start, they are all quite fragile. But the Psyker may just be the most fragile in the beginning of them all.

But after some time, it will improve when you getting some Doctrines and nice items in.

I have two characters and they both are psykers.  My first character with a non seasonal one and he is at level 98. When the new season started I started a new character and he is now at level 71.  The key is keeping the distance open between yourself and the enemies by using ranged weapons and powers.  I also try to use AoE powers rather than single target.  You also might want to pick lower level battles until your character is stronger there are always a bunch of them in the lower level systems.  

It lacks a tool to promote and imagine builds outside the game, a tool to see the passive ones and you can imagine your build, as almost all big arpgs have, titan quest, poe, grim dawn, last epoch, etc.

This is their fault, it is very difficult to find builds for the game, and with a tool like this, many others would certainly appear.

Tons of stuff on Youtube.