Back to the relevance of it all,
Boost - STR, Braver's Drink are all valuable to use in any type of environment. They're almost always up.
Braver's Drink = +15 to All Attributes, A good Boost STR is anywhere from 24-25 STR.
That together is a 39-40 STR boost.
We can't really count them out of the picture.
The relevance of pieces such as Ace's Mail is in fact applicable, but only to Stardiver in this case.
It's better suited for 6 hit DRG however, not so much for 5 hit DRG since they are so STP dependent.
When it comes to Stardiver, STR is a very key and important attribute, more so than ATK which is why Ares's Body while is a nice place holder till Ace's, still falls behind Ace's.
A huge perk Gungnir DRG has is the ridiculous Accuracy on the Polearm. Which allows them to pretty much neglect accuracy in other gear slots for better, more damaging pieces.
Another big reason as to why 6 hit is important to note in all of this is due to the fact that an ideal Stardiver set cuts out quite a bit of STP. Some may require that bit of TP in order to even complete a 6 hit.
At this point, one of my biggest wonders is what type of Grip would be most applicable for Stardiver. Till now I've been utilizing Claymore Grip, since it regardless of the fact that Stardiver isn't Crit I still gain +3% Crit Rate, on top of the ~+7 Crit Rate I gain from it.
Last thing to consider is BRD.
BRD will provide a STR Boost as well if you have minuet up.
So as you can see, that would push it up to what...? +49-50 STR When buffed appropriately, bringing Ogier's back into it's playground.