That's arguable, because there is, while the details may vary, a general idea or consensus on how things work, usually based on existing canon material and the official GW codices.
Given reactions I've witnessed across several forums, I'd rather say there are several consensuses, depending on the vocal majority and what sort of (mis-)information they've been spreading.
We all know (I hope), that the material is conflicting when it comes to a lot of details, yet depending on where you look, people propagate a specific interpretation as "The One Truth", either because it's the one they like most, or because it's the only one they know. Word of mouth then leads to it catching on. Unfortunately, the Lexicanum wiki is a major culprit here, as it is often referenced as a source even though much of its content is biased due to how the individual editors chose to incorporate the material.
And then, of course, there is the common ground propagated in the official material, though I'd say it is far smaller than a lot of people seem to believe.
In my opinion, the worst case is when one of these "community consensuses" actively ignores the contents of the original codex material. Even though those writings are no more "right" than any other product, it's always sad to see when its existence is not even acknowledged. And from what I've seen over the years, a large number of fans is woefully unaware of what their favourite army's codex says. Just take the many discussions about Chapter size, for example.
I'd disagree, because going by pure mechanics, a Bolter is inferior in killing power to two lasguns. There's no lore that really supports this. The bolter is pretty much unilaterally portrayed as being much massively superior, which makes sense given that... well, it fires 20mm armour-piercing explosive shells and the lasgun is a laser weapon that can barely blow off limbs...
Any weapon is inferior in killing power to two lesser weapons, if said lesser weapon is already sufficient to do the job. You can only kill something dead, but not "deader".
The chance to actually achieve this result on a normal human target would be 50% with a lasgun, 66.6% with a bolter. If you say that two 50% chances are better than one 66.6% chance ... I'd say that is arguable and very situational. And, of course, we are also ignoring the boltgun's much better penetration that would in many cases negate an Armour Save.
"Laser weapons emit a beam of focused light. The short duration high energy beam produces such a rapid temperature change on the target's surface that it vapourises in a small explosion."
-- 3E core rulebook
The "a platoon's worth of lasguns can kill a Space Marine" is going by mechanics, btw. The chance for a lasgun shot to kill a Marine is 1/18 (1/2 to hit, 1/3 to wound, 1/3 to get past armour), which means a platoon of 20 men is pretty likely to kill a single Marine with massed lasgun fire by game rules. Fluffwise, the lasgun has pretty much always been portrayed as significantly weaker than it is in mechanics.
"To Hit" rolls have nothing to do with a weapon's killing power. Armour Save and Toughness Save -- that's it. It should be noted that the result corresponds nicely to both the Codex Angels of Death as well as lasguns in the d100 Inquisitor rules (2d6, must roll above 10).
"Against most small arms, the armour reduces the chance of injury by between 50-85%, and it provides some form of protection against all except the most powerful weapons encountered on the battlefields of the 41st millennium."
- 2E C:AoD, Space Marine Power Armour
The 85% end of the spectrum arguably refers to lasguns, easily the most common small arm in the Imperial arsenal.
I don't see this supposed discrepancy between mechanics and fluff portrayal.
Edited by Lynata