The hongmoon weapon & accessories can be evolved and leveled far beyond infernal gear level.
They are the endgame gear and one strives to keep upgrading every time they are able to.
If you’ve seen people with upgraded infernal gear, it was just the hongmoon upgraded versions.
They eventually change into awakened infernal and true infernal, and require materials from the tomb of exiles and general cinderlands area.
Afterwards, when you reach the moonwater plains zone, your hongmoon gear will reflect the weapon & materials from the moonwater plains.
It is similar to how your hongmoon gear turned into awakened and true blight around level 20 when you used the blight gear as evolution fodder.
The current hongmoon weapons can already be evolved lategame into legendary weapons with ability far beyond anything you could otherwise obtain.
I would suggest sticking to the path of hongmoon.
Warlocks are definitely not gimped hp wise, and along with skills such as bastion and their plethora of life stealing abilities, warlocks have very strong sustain for fights with heavy aoe damage.
At max level you can get 70-80k+ without trouble just like the other classes.
Part of it is via leveling, some levels themselves reward over 1k hp, along with other stats.
The most important hp gain however is from your soul shields.
If you’re severely lacking in hp compared to other similar level characters it means you’ve neglected to change your shields in a while.
You can view other players profiles and gear to compare their shields with yours and you can see exactly where they’re getting their extra stats from.
The level 36 purple set from the tomb of exiles instance is generally what people tend to use up until 45 or so, however if all you want is more hp, the defensive shield sets you can purchase with valor stones are also significantly better than lvl 20 or so shields.
Most people don’t really worry about their shield sets up until 45 when solo content like mushins tower, and general pve push you harder and harder to perfect yourself.
Here’s a general chart on the weapon & accessory evolutions and materials if you’re still uncertain about it ~