We HAVE to use the average over time. There is no other way to measure gear vs gear.
Str vs DA rate is almost exactly like my WS choices.
The str grip has more consistent damage. (similar damage gains all the time)
DA is more variable or 'spikey' boost to damage. It does nothing, or it does a LOT (rarely).
I have a Ryunohige. With the 15 or 30% boost to drakes, drakes should average more damage than stardiver for me over time, but its strength over stardiver (for mythic owners) is still based on the crit rate. If i use 5 drakes in 1 fight, it is VERY possible that if i did 5 stardivers instead, the stars would do better if I just dont crit much on drakes. Just like you can use pole grip and on some fights it just wont be better than 4str. But then the next fight i get crits out the *** and drakes rapes stardiver. Similarly next fight you could get a lot of DA procs off grip and it would win handily.
No one in their right mind will say that stardiver is stronger than Ryu's 30% boosted drakes, even if stardiver is more 'consistent'. Just like adding a little str isnt better than a stronger, though less consistent, DA buff.
Heres the problem. We cant predict which way it is going to be before it happens. Because we dont have a crystal ball to see when the random elements like DA, crits and the like will trigger, we cant just adjust our gear. So what can we do about how we gear?
Theres 2 options:
Option 1- Play the safe card. Pick boosts with more consistent output. Str. Atk. Guranteed damage every time you hit even if it will avg less 'over time'. Say a dice roll range between 5-7.
Option 2- Pick the highest performing gear over time even if its variable. Crit rate, DA, QA, Acc etc. Some times a particular stat wont do anything, others it will, but over time you will do the most damage possible. Say a dice roll range between 1-20. 1-20 will avg higher than 5-7.
If you apply the argument you are making to EVERY stat it quickly unravels. Why should I add 10 acc to my TP set? How do I KNOW it will make me land an extra hit since its just 5% hit rate? I can add some str that is GURANTEED to raise my damage instead. You dont know when it will and wont help you because its randomly generated. But you want to do the most damage possible so you make sure you have your acc in check.
Gearing to be the strongest DD is just a giant dice game. Each individual aspect gets a roll with a random factor we cant control. Atk has the giant + - 0.2pdif and the 5% randomizer. Acc is random. can miss twice in a row with capped acc or hit 5x in a row with floored. Crits are random. DA is random. Fight lengths are random. Every aspect of our damage is just roling 10-20 dice every time we swing our weapon.
Gearing to the best of our ability is just stacking the deck in our favor for ALL the dice rolls we do. This whole game is just making your odds of doing what you want (kill things) better. You cant eliminate risk, so you just go balls to the walls stacked deck style and if you tweak enough stats in your favor, you have an EXCEPTIONALLY high probability of winning.
Separating out singlie aspects and saying "I REFUSE TO BE RANDOM about THIS ONE THING" doesnt do anything but turn your overall odds of doing more damage down. Instead of rolling a number between 1-20, your saying "i dont like the randomness" and making the roll 5-7. Sure you never roll a 1, but you are giving up 8-20. In the end your just hurting yourself for the sake of 'consistency' in a monsterously random world.