I think its important to bear in mind that a base autogun and a base lasgun are similar in performance, its only when you add special ammo onto auto weapons that they excel. And you can add mods onto lasguns too, so they CAN compete.
But guess what, las-weapons are cheap to manufacture and maintain and are thusly produced in the trillions of units to equip the countless forces of the imperium. Those forces with no technical aptitude, who often don't have the resources or time to wait on bulky specialized ammunition to arrive at wherever they are operating.
I mean if funding and resources wasn't an issue then all of the forces of mankind would be equipped with boltguns and power swords. But it is an issue, and when resources get stretched thin and supply lines broken i would much rather my forces be equipped with rugged lasguns over autoguns that may well do a bit more damage but will jam more often and run out of ammo far quicker.
Also bear in mind that an average Imperial guard 'unit' is the platoon which will have anywhere from 15 to 50 or more men, who will each have a lasgun of some sort, who can each burst fire for MANY shots. Many will miss, but they will supress an enemy. Some will hit and of those hits some will critically hit (which always does a minimum of 1 point of damage - even to a space marine, a daemon or whatever
).
So yeah, the lasgun really is represented quite well in RT.