Ok, here's a real simple idea.
Really a lot of the problem with the smaller AC's is they really don't have an effect in the Anti-Mech role,
while they do have utility in other areas (AAA, motive crit seeking on vees, Long Range Anti-PBI with flechette, etc).
So let's add an effect directly targeting 'Mechs.
Remembering back to some discussions on the old forums on ways to address flashbulbs being too good in the DHS era,
there was a suggestion that energy weapons should create less knockback on figuring PSR's. The idea was shot down
a bit for game balance (and the physics of it), but let's take the idea and flip it.
The rule change: Each standard/precision/AP salvo of slugs adds the equivalent when calculating PSR's, of an additional two points of damage in single shot mode
or per shot in Ultra mode. Rotary Autocannons add the equivalent of one point of damage per salvo when calculating PSR's, at all firing speeds.
Where does that get us?
AC/2, LAC/2, LB 2-X: Would still take 5 of them (instead of 10) to force a PSR. Still, the pressure adds up on some designs, like the Mauler or a pair of Pikes.
Ultra/2: Would still take 2 1/2 of them on Ultra to force a PSR, but it would be able to add pressure.
RAC/2: Going full bore, one would be just short of being able to force a PSR. Becomes an eight ton pressure weapon instead of an inefficient SRM alternative.
AC/5, LAC/5, LB 5-X: Would take 3 to force a PSR instead of 4. A pair with a LL would make a knockdown combo.
Ultra/5: Still would need a pair on Ultra to force a Knockdown, but one UAC/5 plus an LL could make a good combo.
RAC/5: By itself, PSR chances don't change at a given firing speed, but it can help at lower fire rates with additional weapons.
AC/10, LB 10-X: Add a Large Laser and we've got a knockdown.
Ultra/10: Not much help in Ultra mode, but as with above, a Large Laser and a single tap would be a knockdown check.
AC/20, LB 20-X, Ultra/20: The extra knockdown points don't do anything in these cases normally, but with Hardened and Ferro-Lamellor armors on the field,
it can help make up the difference for the lost damage.
Looking at some canon units:
-The JM6-S JagerMech,and -4R and -5D Enforcer, would now be capable of generating a PSR at range.
-The -3N Rifleman would be able to force a PSR at range with the AC's and one LL, instead of having to fire both LL's. The -5M model can force a PSR check separately with each arm.
-The ON1-K Orion can generate a PSR at range with the statistical average 9 missiles of the LRM-15 hitting, instead of needing needing a better than average roll on the cluster hits table.
-The RAC/2 Variants of the Templar and Pike become downright scary, being able to generate well over twice what is needed for a PSR check, or give three 'Mechs close to
PSR levels of damage.
-Way at the other end of tech, the Standard Bane can generate a PSR easily instead of having all the UAC/2's hit perfectly in Ultra mode, and can actually force a second PSR
check on a separate target if everything hits perfectly.