You don't need to race a Ferrari against a Prius to know the Prius will lose.
By that logic, a broken down Porsche with no fuel, a broken axle, and no tires automatically beats a Prius with an engine swap and full customizations when you race them. The ReLL will do 9 damage when it hits any unit, including one with Ferro Lamellor and reflective. A large laser may be lighter, but it'll still only do 4 damage to the reflective and 7 damage to the FL unit. Two of those LL's are ten tons, and each requires a to-hit roll. Fail one, and you're doing less damage than the RE laser.
The RE laser doesn't replace standard or pulse lasers, as it wasn't meant to. What it does is give units facing anyone with specialty armor a weapon that'll poke holes in it. For an aerospace fighter, I'd expect these to be rather useful, especially given how quite a few units got reflective armor, and it keeps the ammo tonnage available for other, longer-ranged weapons. Or room for fuel. For scouts, it's also something that could be useful, and maybe as a space-filler in an assault.