I believe the Lascannon is 2 seconds, MC Lascannon is 1.5 seconds and Burning Light is 1 second. But generally speaking you will lose most CQC fights against melee or a bolter, yes.

A fire mace (subfaction and class specific) is a long shot from a poison chainsword (TA/Rap regardless of warband or mark).
1. maces aint great in current melta
2. melee healer is a bad idea. CSM (you) should know best
3. slow weapon + DoT that doesn't bypass armor

So no, they have it but they don't. Which is why dude asked for a LSM DoT chainsword specifically back.
Which I neither supported nor bashed (hint: I don't support it)

Seen guys do Burning Light CQC, got a successful hit and was still cut down in melee before the enemy burned to death.
Using a 1 second charge up one-shot weapon that can do jack when face-charged is an extremely poor example of an "effective DoT weapon".
But it's Katitof, so nothing new here.

Here's a thing: Both the Napalm Kannon and the Burning Light Lascannon actually inflicted a 1 second stun after they successfully hit someone. After the mundane Kannon got nerfed, the stuns of both weapons vanished. This stun was essential to the working of these ailment weapons, as without it the enemy can immediately just roll to delete massive chunks of the ailment, as shown here:

Other stuff aside, Mancatcher and LSM unique mace are actually quite amazing and are my default GA weapons since they were implemented.
They both are REALLY good.

And the dude can have LSM DoT chainsword the very moment warlock and sorcerer will have proper ranged weapon that doesn't use same resource as healing, painboy can have proper weapons at all, all 3 other factions can get sniper rifles, chaos and orks can have potent damage resistance buffs or debuffs that doesn't require 100% time commitment from support, all other factions can have weapons that can snare everything and are anti-all and so on.

LSM isn't getting other factions unique toys without sharing their own.
Until that time, if someone wants to play with flame or poison melee weapon, go for non LSM faction.

There should be a line drawn on LSM wanting other factions stuff without wanting to give out their own.

Who on earth would want gravity weapons lol

I don't see what the fuss is about. Ailment melee weapons don't shorten the TTK, at best they just make it less likely someone will flee and survive.

Only place I'd want an ailment weapon is for PvE when dealing with Warriors. Narthecium's poison works.

Happily see them on Eldar. Nothing like a Grav Gun to slow down Ork melee.

Clans often use the cannon variety, paired with multimeltas to catch and destroy moving transports.

Hawks with Grav-guns to snare vehicles for Fire Dragons.