Precision weapons are the only Ranged weapons that matter.

[NaijaMan]

ditto

[Grrwaaa]

They all have their purpose. Assault weopons can stack lethal and focus and just maul groups all at once with auto-fire. The light weapons have a bunch of debuffs that can augment a support character.

[Kyoken]

Purely about damage, yes precision wins out, however assault weapons are great if you stack lethal on them because each hit has a chance to instantly kill the enemy. and light weapons have lots of buffing/debuffing attacks that are useful.

So far only the spread weapons seem to be useless at endgame.

[Fluxit]

I find them pretty balanced and used all of them in different teams (2 playthroughs with GOG version).
- Assault: Stack focus and burst attacks to do absurd damage vs bosses. My favourite in endgame.
- Light: Diverse bonuses like +scan, purge, track, vulnerabilty, ... not for damage. I use it if I find good equipment, e.g. on strategist to apply the 6% focus for the group on high prio targets.
- Precision: High damage that goes well with added extra shots and burns. Good vs armour.
- Spread: Fastest application of debuffs or lethal. Good if your champ usually does different things.

[Kaerius]

Aside from lethal, assault weapons are also great for applying debuffs like fear, stun, etc.
Spread is also useful for debuffs, spreads the chances so you can debuff multiple targets, while assault is more reliable for debuffing a specific target.
Light is almost pure support... it can be good to have on a support character to have access to things like purging shot.

Sidenote: endgame, special abilities outshine weapons by a mile. Especially from subclasses like Psyker and Demolitionist. A tracker/demolitionist is just epic destruction on anything that doesn't have high evade, and a psyker can deal with those. Bring a medic along to energize them, and you've got a team that can kill off many encounters before they have a chance to attack you.