I get that Particle Beams don't have any damage fall-off at range, but is that enough to make up for their size and relative weakness to lasers on paper? At 30,000RP in all relevant techs, I can get a Laser a little smaller and a little slower to fire compared to a Particle Lance with a range of almost 4 million km and damage output of 65 compared to the Lance's 18 damage. I know you can't take full advantage of the Laser's range, but 4 million max range means the damage falloff is much less severe making the heavier Particle Lance kinda pointless.
Thing is, at long ranges armor will stop lasers dead in it's tracks - not the case for particle lances. Against unshielded but heavily armored targets, particle lances are very strong at long ranges. Even with high max range on the laser, because it does reduced damage and doesn't shoot in a straight line, you will to less damage to armored targets than a particle lance would.
However, in general I agree that either lasers are too strong, or other beam weapons are too weak. If you want the most powerful fleet the only choice really is lasers and missiles with gauss if you don't want to use AMMs.
There is also a significant contribution from BFC range. Maximum weapon ranges tend to increase quadratically* while BFC ranges increase linearly*. At some point you will regularly have laser with ranges exceeding your BFC range. Particle beams are actually an exception to this as their range increases linearly but in general they are just short of maximum BFC ranges at each tech level, though by exactly how much varies. This means that despite the very long weapon range of lasers, in practice their range will be limited to about 15-25% beyond the range of a particle beam, and in this part of their range accuracy will fall off to 20% or worse, compounded by damage falloff especially at lower tech levels.
*Actually it's more complicated than that since the gain from tech is geometric, but that is not the important part here.All together, this means that the lasers have an advantage against particle beam ships if they can kite them by being faster; however, if the particle beam ship is faster it can keep the lasers at maximum range and take advantage of their lack of damage falloff (and, with Lances, superior penetration to boot) to out-DPS the lasers. At close range the lasers probably win by sheer DPS.
In a direct contest between lasers and PBs, the lasers are probably better just because they are more flexible as long as you are winning the propulsion arms race. However it is very difficult to beat the long-range alpha striking and penetration of a Particle Lance on a fast ship, and particle beams complement Railguns quite well which mitigates their short-range DPS problems. Given this, and the fact that the "main weapons" triangle goes as missiles > lasers > railguns > missiles (all three of these are capable of serving as a fleet's only weapon system including point defense, although they fill different roles to different degrees of effectiveness), I think particle beams are well-suited as they currently are if you think of them as a secondary rather than primary weapon.