Following your questions I decided to run some numbers because I wanted to test it to see if I was correct.
What I am going to assume here for the math is a situation in which you have a large number of CA and are intentionally slamming them into enemy units (meaning the front line of them would be using melee while the rows behind them are shooting). If you want to keep your distance there would be no significant difference between CA as they are now and with the change I’m proposing (meaning only when fighting at melee distance matters).
CA vs Heavy Cavalry
III
Ranged: 13 attack +20% (vet) x3 = 46.8 damage per shot.
Melee (After Sonyna): 6.5 +20% (vet) +5 (Sonyna) x4.5 = 57.6 damage per hit.
IV
Ranged: 13 attack +85% (vet +Tatar +Cav Combat and Arsenal up) x3 = 72.1 damage per shot.
Melee (After Sonyna): 6.5 +85% (vet +Tatar +Cav Combat and Arsenal up) +5 (Sonyna) x4.5 = 76.6 damage per hit.
V
Ranged: 13 attack +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) x3 = 91.6 damage per shot.
Melee (After Sonyna): 6.5 +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) +5 (Sonyna) x4.5 = 91.2 damage per hit.
Most heavy cav have ranged resist so the melee is even better and I’m not counting the AOE on the melee either. This is a significant win for melee
CA vs Goons
III
Ranged: 13 attack +20% (vet) = 15.6 (or 17.5 with Cav Combat) damage per shot.
Melee: (After Sonyna): 6.5 +20% (vet) +5 (Sonyna) = 12.8 (or 13.7 with Cav Combat) damage per shot.
IV
Ranged: 13 attack +85% (vet +Tatar +Cav Combat and Arsenal up) = 24.0 damage per shot.
Melee (After Sonyna): 6.5 +85% (vet +Tatar +Cav Combat and Arsenal up) +5 (Sonyna) = 17.0 damage per hit.
V
Ranged: 13 attack +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) = 30.5 damage per shot.
Melee (After Sonyna): 6.5 +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) +5 (Sonyna) = 20.2 damage per hit.
Here when the Dragoons 20%RR is taken into account its a tiny win in melee in age 3 before cav combat. I believe fighting at range wins in the other scenarios outlined above, though I didn’t count the AOE and snare matters here as it delays the ability of the goons to run away. I’m going to count this as a loss for the change I suggested.
Of course if you don’t get close enough to melee you’re using range and that will be the main situation here meaning the suggested change doesn’t lose you very much.
CA vs Musketeers
III
Ranged: 13 attack +20% (vet) = 15.6 (or 17.5 with Cav Combat) damage per shot.
Melee: (After Sonyna): 6.5 +20% (vet) +5 (Sonyna) = 12.8 (or 13.7 with Cav Combat) damage per shot.
IV
Ranged: 13 attack +85% (vet +Tatar +Cav Combat and Arsenal up) = 24.0 damage per shot.
Melee (After Sonyna): 6.5 +85% (vet +Tatar +Cav Combat and Arsenal up) +5 (Sonyna) = 17.0 damage per hit.
V
Ranged: 13 attack +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) = 30.5 damage per shot.
Melee (After Sonyna): 6.5 +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) +5 (Sonyna) = 20.2 damage per hit.
Here fighting at a distance where melee is possible will be bad in most situations, so the change I suggested matters little since you’ll want to avoid getting that close. This will basically apply to all heavy infantry.
CA vs Skirmishers
III
Ranged: 13 attack +20% (vet) = 15.6 (or 17.5 with Cav Combat) damage per shot.
Melee: (After Sonyna): 6.5 +20% (vet) +5 (Sonyna) = 12.8 (or 13.7 with Cav Combat) damage per shot.
IV
Ranged: 13 attack +85% (vet +Tatar +Cav Combat and Arsenal up) = 24.0 damage per shot.
Melee (After Sonyna): 6.5 +85% (vet +Tatar +Cav Combat and Arsenal up) +5 (Sonyna) = 17.0 damage per hit.
V
Ranged: 13 attack +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) = 30.5 damage per shot.
Melee (After Sonyna): 6.5 +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) +5 (Sonyna) = 20.2 damage per hit.
Fighting Skirms with CA isn’t a great move, but given the 30%RR, melee wins in both age 3 and 4 even without counting the AOE or snare. In age 5 it’s a very small win at range without counting the snare or AOE, it’s likely small enough that melee wins by a tiny margin.
CA vs Artillery
III
Ranged: 13 attack +20% (vet) x2 = 31.2 (or 35.1 with Cav Combat) damage per shot.
Melee: (After Sonyna): 6.5 +20% (vet) +5 (Sonyna) x2 = 25.6 (or 27.5 with Cav Combat) damage per shot.
IV
Ranged: 13 attack +85% (vet +Tatar +Cav Combat and Arsenal up) x2 = 48.1 damage per shot.
Melee (After Sonyna): 6.5 +85% (vet +Tatar +Cav Combat and Arsenal up) +5 (Sonyna) x2 = 34.0 damage per hit.
V
Ranged: 13 attack +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) x2 = 61.1 damage per shot.
Melee (After Sonyna): 6.5 +135% (vet +Tatar +Imp +Cav Combat and Arsenal up) +5 (Sonyna) x2 = 40.5 damage per hit.
Here if you take into account the 75%RR most artillery have it’s a big win for every CA that gets to use melee.
CA vs CA
This is a win for the CA without Sovnya with the change I’m proposing if you get into melee range.
In all the change I proposed helps against Heavy Cavalry, Artillery and to a lesser extent Skirmishers that have a 30%rr or higher.
Against Heavy Infantry it’s bad if you get into melee, but that’s bad already so staying at range is best.
Against Ranged Cavalry it’s a negative from a damage standpoint in most cases. You’re more likely to snare which is good, but this is a negative overall, I think.
Having stated that, I think Russia benefits more from CA being better against Heavy Cavalry and at snaring enemy units than it hurts them against Goons and Heavy Infantry imo