Not Tachyon Lance, that thing is powerful enough.
Every other beam weapon though, particularly Tactical Lasers and Graviton Beams, ESPECIALLY Gravitons, simply don't do enough damage. I realize that they can function for zoning AI, but considering how weak they are that seems more like an exploit/bug than a proper feature. If the AI were smart, it would simply ignore those beams completely. Even without shields, Tactical Lasers aren't really a threat, even focusing several on a frigate can take upwards of 10 continuous seconds to kill. Gravitons are even worse, since they practically only do "damage" to shields, and that damage is so low it would be negligible as a small mount at half the cost.
I've been testing with (most) beams modified for 2x to 3x damage and they still feel kind of weak, but once in a while they can actually hurt something so maybe that's good enough. As a mechanic soft flux is so much less effective that I think it deserves to be much more efficient in terms of cost to fire, and this sort of multiplier seems to work alright.
Edit: For the most part I don't actually use beam weapons on my own ships, except the Tachyons. My testing mostly consists of seeing what it feels like to go up against beam-heavy enemy fleets. Without changes, they are so pathetic I actually feel sorry for them.