Toxic flamethrowers aren't flamethrowers. They are weapons that can launch liquid toxins on distance creating toxin spills as I suggested in another thread. Grenade with elemental damage are absolutely ok.
"Real" flamethrowers are flammable-liquid chemical throwers with an ignition sistem and have also a commendably long range, the gas one (which i think is the one you reference) doesn't really exist as a weapon, chemical throwers and flamethrowers, excluding the eventual ignition and anticorrosive coating depending, they're exactly the same device.
Toxic damage would be toxins and acid. Acid corrodes armor and toxins melt flesh. That's why they are very effective on infantry. Ice doesn't really affect armor at all, the point of freezing to the point of being crushable is to freeze water. Armor has no water. As for the insulation, you are right, however it's a game, why not? I see no point in thermal being effective against armor, it stops heat really well if heat isn't constantly applied for long time. Kinetic has penetration simply by giant force, nothing else has it. That makes kinetic effective against armor and shields. Beam is really a concentrated heat. So while good vs armor after a bit of melting, it can be useful also against shields. Shields often stop energy and ignore kinetic, why not here?
It's an arbitrary sistem becouse a good half of those things doesn't exist but still teorycrafting it i disagree
first off, everything is extremely effective against flesh unless you're talking about elephant/t-rex flesh which is so thick that we might as well call it armor at that point so what's effective against flesh is a bit beside the point.
Second, shields can block everything and the opposite of everything depending on lore (assuming they exist) so they're left as balance fillers for thing that aren't effective against armor.
"Ice" and "cold" are very different things, you cannot weaponize ice (well you can but it'd be kinetic damage at that point =) ), cold not only makes armor brittle but also bypasses it (generally through ventilation/direct conduction), cold affects the structural integrity of metal, a termal shock combined to sending armor far under the ductile-brittle transition temperature is guaranteed to make it shatter like glass, at which point if what's inside isn't already dead it'll soon be, besides intense cold causes instant tissue necrosis on the affected parts, water in the body freezing isn't generally the cause of death and is technically survivable.
Thermal is similiar in most aspects to cold and bypasses armor in similiar ways
Kinetic damage is the least effective thing against armour that you could think of, in terms of results/energy spent, armor's motive of existence is deflecting kinetic energy, you can puncture armour with enough kinetic energy but it's a very inefficient process given that simple puncturing isn't nearly as damaging as cryogenic/thermal/toxic burning, besides 99.9 of armor piercing ammunitions are also either incendiary, explosive or pyrophoric
The thing I meant is that beams are damaging the target because of heat they produce. They have no bullets or explosions so they have to damage by heat applied to target. I was not clear, sorry, what I meant is that beams are damaging with heat, they are ofc not heat by themselves 
