I am changing the values of 280 and 140 to 180 and 90 as they both have the same mathematical difference division wise. Primal Kyogre has a Special attack stat of 180. It can learn Signal beam, a non stab 75 base power move. Nice. Now, let's see beedrill. It can learn giga impact, a non stab 150 power move. Now, let's test this on Boufallant. Boufallant has equal defenses and does not resist any of the moves. I am going to give it no EVs at all, and also, I will be giving it a neutral nature (a nature that doesn't boost any stats). Now, let's look at this. I won't be investing any evs into the attackers.

0 SpA Kyogre-Primal Signal Beam vs. 0 HP / 0 SpD Bouffalant: 50-59 (29.4 - 34.7%) -- 7.3% chance to 3HKO

0 Atk Beedrill Giga Impact vs. 0 HP / 0 Def Bouffalant: 55-65 (32.3 - 38.2%) -- 96.3% chance to 3HKO

Now, as it seems, this means that the higher power move is what matters. But, this answer doesn't satisfy me at all. I'm going to run another test, however, it will be using Deoxys (180 Special attack) and Raichu(90 Physical attack). Deoxys will be using signal beam (lol) and Raichu will be using Giga impact (lol). (Side note: Even though raichu cannot legitimately learn giga impact, I think, the calculator that will be linked allows a Pokemon to use any move) Anyways, here are the calcs:

0 SpA Deoxys-A Signal Beam vs. 0 HP / 0 SpD Bouffalant: 50-59 (29.4 - 34.7%) -- 7.3% chance to 3HKO

0 Atk Raichu Giga Impact vs. 0 HP / 0 Def Bouffalant: 55-65 (32.3 - 38.2%) -- 96.3% chance to 3HKO

So as we see, the base power seems to be the defining variable. However, what if we adjust the base stat ratios just a bit? Let's see how that turns out. Let us use Mega Diancie (160 SpAtk) and use Pidgeot (80 Atk). Now, we can change the move powers just to vary the experiment even more just to really prove our point. Let's say Diancie is using round and Pidgeot is using power whip (again, even though it can't learn it, I can use it)

0 Atk Pidgeot Power Whip vs. 0 HP / 0 Def Bouffalant: 39-47 (22.9 - 27.6%) -- 69.7% chance to 4HKO

0 SpA Diancie-Mega Round vs. 0 HP / 0 SpD Bouffalant: 68-81 (20.5 - 24.4%) -- guaranteed 5HKO

So again, we see the power of the move just barely being more influential. Therefore, the power of the moves are what I see to be the mathematically defining feature.

This is the calculator I used

Hope I helped!