Oh I'm no sire, I'm just a humble peasant scrub

thank you for your detailed reply as well.
Yes, now I see your issue. I use the standard PS4 controller so for me there's no option, I only have the R1 and R2 buttons. With your controller however, you have four additional buttons which makes you hold the controller differently and react in different ways, so for sure it complicates things.
I use right index finger on R1 and right middle finger on R2, and left middle finger always holding L2 (guard stance). When I want to do a zone attack, reflexively I have to use two fingers on the same hand. In your setup you have to use both hands for a zone attack. Unless you're incredibly ambidextrous (I know I am not, hah) then this complicates it even more. Added to the fact that on S4 patch in November, zone attack input became more wonky...
I like how you input the guardbreak, you can slide your index right onto that extra button without really releasing touch from between the Rb and Rt, that's smoother than me having to move my right thumb from the right analog onto the square button. Though in my case GB = bash from neutral / bash cancel into GB (Warden), and quick side dash using X button, into GB (Raider), they're the two heroes I use the most and I feel the default setup is what befits them the most.
I have L1 assigned as sprint button (the quickchat became the analog L3), and toggle turned off (must hold L1 to keep sprinting). I mostly use the first set of templates. It's still somewhat wonky because my muscle memory knows the L3 to be the sprint, but I felt holding L1 to sprint was a bit more reliable.
However I see something with the Razer Wildcat here. Notice the standard PS4 controller L2 and R2 buttons:

You see there's a single angled surface on which to apply the pressure when pressing the button. On Razer Wildcat I see two angles, one being frontal, the other being the outer corner. I'm willing to bet the outer corner angle has worse pressure detection and more often than not you'll end up doing a light attack using M3 instead of a zone attack.
Could you try changing the M3 button to a heavy attack input? see how it works, maybe it'll be easier to pull off. Maybe it could go better with the M4 seeing as the M4 is the feint button. I think the problem with controllers is that they require a certain push-in distance to register the attack in For Honor, and since during a zone attack the R1 / Rb buttons have smaller push-in, we'll mess up our timings mid-combat when we press R1 (Rb / M3) and R2 (Rt) quickly. And in your case with Razer Wildcat, if you hit the corner angled surface of the Rt by accident, it'll be even more inconsistent.
I agree that the zone attack input in general is being too flimsy on controllers, because of the R1/Rb and R2/Rt combinations, because of the push-in distance. They definitely should increase push-in detection on the R2/Rt button.
Yeah I do think that's where things got messed up, by fixing some zone flicker they reduced the swift input detection and created these input problems. Also I've noticed it on dodge as well. Sometimes my character just won't dodge the exact moment I press X.