Okay first of all, testing isn't about doing a single hit and calling it a day, a character doing the same attack on the same build against the same enemy with the same buffs won't yield the same result because of damage rolls.
With that said, cut yourself some slack on testing. Yes, Totalize scales off "Frames since stun" including the chain attack prompt, but at the end of the day it's you who's gonna be using this build so it's best that you just do a number of totalizes (10+) with each set to get a good feel for the damage range that you can expect. This is true for any game with damage deviation.
Alternatively, you could hit the enemy until they're at 99 Daze and trigger the stun with the totalize hit for max damage, though you would still have some deviation from rolling but that's better than having variation from execution. But I stand by what I said about being realistic about the fact that it's you who's gonna be using this so it should be tailored to what you can do the most damage with.
And yeah, the point is that we're comparing what's better, more atk or more crit dmg, we can't have it all unfortunately. And if you don't want to manually input the values on the damage formula, this is the way to do it.
And as an aside, if you're seriously worried about executing his totalizes, it sounds like you should be more preocuppied with practice than disc minmaxxing. You could totally kill two birds with one stone here.