Don't know how much others use mesons, but I do. They work well enough against NPRs and swarm as the only weapon. Didn't get close enough to precursors to test, because I didn't have enough PD to handle their AMM swarm.
The armor retardation tech is maybe best thought of as the percentage of armor that needs to be chipped away before it's possible to start dealing internal damage.
Mesons can be turreted like lasers and gauss, which makes them an ok early game weapon that can be used against both ships and missiles, although lasers would be better against ships and gauss against missiles. Against shielded enemies, they are effective even in late game, when shield regeneration rate can outpace laser's dps.
Wondering, what would be a good damage dealer to got with mesons, I ended up comparing dps of max tech weapons at different ranges:
Weapon | ROF | 100 000 km | 200 000 km | 300 000 km | 400 000 km | 1 000 000 km | 1 200 000 km | 1 400 000 km |
Railgun 50 cm | 15 | 4. 80 | 2. 40 | 1. 60 | 1. 07 | 0. 27 | 0. 27 | 0. 27 |
Particle beam 50 | 25 | 2. 00 | 2. 00 | 2. 00 | 2. 00 | 2. 00 | 2. 00 | 0. 00 |
Particle lance 100 | 65 | 1. 54 | 1. 54 | 1. 54 | 1. 54 | 1. 54 | 1. 54 | 0. 00 |
Laser 80 cm | 35 | 4. 80 | 2. 86 | 1. 91 | 1. 43 | 0. 57 | 0. 46 | 0. 40 |
Laser 100 cm (spinal) | 55 | 4. 76 | 2. 85 | 1. 89 | 1. 42 | 0. 56 | 0. 47 | 0. 40 |
Laser 120 cm (adv. spinal) | 80 | 4. 71 | 2. 83 | 1. 88 | 1. 41 | 0. 56 | 0. 46 | 0. 40 |
The particle lance is supposed to have similar damage profile to a laser, and the 120 cm, 100 cm and 80 cm lasers match the 100 damage at 450k km, 312k km and 200k km respectively.
Based on these, against unshielded enemies, at long range the particle lance probably owns, as it can punch through armor and there's enough damage left to blast most of what's underneath. Against shielded enemies, at medium to long range, particle beams are best. At short ranges lasers are best against both shielded and unshielded enemies.
So, lasers for jump point defense, particle beams for long range combat against enemy beam ships and enemies that are hard to catch up with.
Also, shields regenerating 5 strength per second are recharging faster than any beam weapon's dps.
IMO, the biggest problem with beam weapons right now is that the fire control range doesn't keep up with the weapon range. E. g. 20 cm UV laser on spinal mount has max range of 640 000 km, but you need fire control range tech 150 000 km to get even 600 000 km max range. Maximum range for beam fire control is 1 400 000 km, but max tech mesons have range of 10 080 000 km, and you can have 30 cm mesons firing every 5 seconds at range of 1 440 000 km. I. e. meson focal size tech after 30 are redundant (unless you want mesons that don't fire every 5 seconds, but what's the point of that?). A max tech laser in advanced spinal mount has range of 45 240 000 km, over 30 times more than max fire control range.