I agree with your conclusion, but not your starting point. Actually, accuracy is a function of weapon length [or even more in detail, the distance between the rear sight and the end of the barrel/front sight]. A long barreled sniper type will be the best. The assault type weapons should be midway between the sniper and the SMG type. Machine pistol and pistol type will be the worst.
That only takes into account the sights' accuracy, in which case many telescopic sights are the most accurate (if adjusted properly), but not very long front to back. A longer barrel is more accurate in practice because it allows for more tolerance in sighting: if the front sight is adjusted a millimeter too much to the left, it's a bigger angular difference with a short barrel than a long one. A longer barrel also allows for more support to be applied, e.g. a two-handed grip. Also in play are dimensional and positional tolerances of parts. A sniper rifle (these days) is machined to much tighter tolerances because it must be accurate. SMG, not so much, so they allow a little more slop, which makes it much cheaper to produce, incidentally.
More power leading to better accuracy is only accurate with ballistic rounds. More power means higher speed, which means less drop at a given distance due to gravity (can be compensated for). More power is usually accompanied by greater projectile mass, which helps in the stability of its flight -- wind can't push it around so easily, imperfections in the bullet (uneven weight distribution) don't count as much. Since laser beams are massless the point is moot in both cases.
In the end laser (and other beam-type) weaponry is inherently more accurate than kinetic weaponry just because it is easier to manipulate light on a precise and consistent basis than matter. A rifle clamped to a very heavy base (to make recoil a non-issue) and fired four times at a target will show, in most cases, four different impact points. There's a lot of random stuff that can happen in the shell casing, propellant, slug, barrel, path to target that change the course. A laser, you clamp it down, and flash it four times, it'll hit the exact same spot four times.
In other words, laser accuracy is limited to human skill, where it's not necessarily the case with ballistic weapons. That said, human accuracy is generally better with long arms. My proposal is this:
Pistol: middle-of-the-range accuracy, both snap and aimed. Kneeling doesn't help much, since it doesn't stabilize the weapon itself.
Rifle: decent accuracy at snap, a little better than pistol. Aimed, it goes even higher, since here there is actually much room for improvement. Kneeling helps even more.
Heavy laser: It's big and awkward to carry and aim, so lowest accuracy while standing. Probably so unwieldy that a snap shot could go anywhere, but an aimed shot should have
some chance of hitting its mark. Crouched, support really helps. Probably has a bipod under the barrel. Final accuracy is better than the pistol. If it's meant to be a support weapon ala M249 SAW (machine gun) final accuracy when crouched should be between pistol and rifle. If it's meant to be a sniper-type weapon as mentioned by Surrealistik (still a support role) then accuracy should definitely be highest, but only when crouched!
I do agree that the laser pistol and rifle are pretty well balanced (except for the accuracy cross), but the heavy laser isn't. Currently I never use it because the damage isn't really that much, TU usage is horrendous, and the magazine is tiny.
