Some enemies have reistances against everything, with the lowest resistance being at 70% up to 99%, they walk with 90k HP
now times who knows how many enemies, just makes this not possible to deal with

do you have a plan on making a weapon mod or something?

To be honest, what I read does not correspond to any type of resistance.
Minor resistance: 35 --> 65%
Major resistance: 80 --> 92%
Extreme resistance: 99,99%
unknown damage type (for example K2 "radiation", bob-warfare "plasma"): 0 --> 70%

Usually, faction has only one Major/extreme resistance or immunity + resistance to unknown damage types.

One faction, the "Juggernauts", has extreme resistance to fire and phys. damage. They need to be killed with a laser or damage with a type of mods.
Their development turned out to be a forced measure, because otherwise a mix of flamethrowers and three rows of ammo-turrets destroyed any combination of enemies

Also, now I am watching the stream of "K2+SE+rampant fixed"+some utility mods, where the player perfectly beats ~85-90% evolution at the pre-cosmic stage

Perhaps you can give a concrete example?

the best ways to kill factions:

T1 Common: anything
T1 Acid: non-acid damage
T2 Laser: fire, physical
T2 Electric: fire, physical
T2 Fast: any short range defence (range < 20)
T2 Suicide: any rapid-fire defence
T3 Wasp: anything
T3 Spawner: any area damage
T3 Regenerative: fire
T3 Sapper: fire, physical
T4 Fire: laser
T4 Brutal: laser
T6 Inferno: the best is laser, but anything non-acid/fire works fine too
T6 Poison: the best is laser, but any non-fire direct damage is good
T7 Nuclear: any rapid-fire defence
T9 Juggernaut: laser, electric

So, you will not be able to do only with flamethrowers and only laser protection. You need a mix.

As for weapon mods, Rampant Arsenal does an excellent job with the eighth level of enemies. But even there, a mix of protection is needed, although many layers are not required.
If you add to this mods for turrets-veterans, shields, then you can even play at level 10. If resources are available

Also, an important feature of any Rampant is that a small base is deadly.

It is necessary to kill the biters while they are weak, freeing the territory of possible pollution and key resources