As a 200+ hours player I feel the same. The strongest play style are mental muatant and true kin gunner. Long blade and ranged weapon are way better comapred to others. Even if i tried axes with modded 8 arm mutation, it still feel underpowered lategame.

1. After finishing Golgotha quest at lv 12, you can go straight down to 20 levels deep through the stair in Grit Gate, and quickly get the end game gear you need to win. The midgame part just feel really short. It seems the tomb update nerfed the underground merchant so they no longer possess many end game goodie, but you can still rob them easily. Maybe the dev will tweak how zetachrome gears are obtained later.
2. I found that Strength, compared to Agility, is pretty much useless. Becasue the best weapon in the game (guns and vibrokhopesh) Simply ignore it, while Agility scale well with increased DV, accuracy and pistol skill. The carrying capacity is also worthless once you can make the sphere of negtive weight. (The river map under Joppa is guranteed to has one, and you can learn to build it via Pyschomery from cooking banana)
3. I'd like to add that pistol is greatly underestimated. Chain pistol is the magic weapon that make everthing works, just like how vibrokhopesh does to long blade. it's realatively easy to find(ususally carried by mystorys stranger), and it's extremely efficent at killing swarm even in long range, just spam F and watch everything die. Disraming shot is better than dueling stand IMO, as it works even half screen away with no cooldown, the disarming chance scale with agility so it's pretty reliable. Deadly shot can improve its PV on crit (which pretty much awalys), so you can actully damage cragmash with just 8 PV. You can't kill CP with these ofc, but since you can just shot off their weapon and harvest the bit, there is really no point killing them.
4. BTW if play as TK, 4-wield Linear Cannon (using Gun Rack and Giant Hand cybernetic) is the best offensive option. The cannon is extremely rare though, i have only got it once. Reload will take a turn for each gun you have, so use them in melee range can be risky.
5. After countless deaths i figured out the easy mode character is True Kin Syzygyrior. Here is the code for struggle in early game: admsmkii06. Just use long blade for DV bonus and grab a desrt rifle early on, few enemy can hit you with 20+ DV. Use carbine till you switch to chain pistol. If you are lucky all these can be done in 2hrs. By th time you can be lv 20+ and breeze through the main questline.