As usual, you are bringing in information I was unaware of. That definitely calls into question my ordering of importance HP/Res for Nat affinity.
In this case, resistances affect incoming damage before absorption is something I didn't know. I always assumed it was absorption that was eaten before any other consideration outside of whether or not you were hit. This is the case in many other games and it just creates a much less valuable, apart from all your personal defenses, shell of fast eaten HP.
So since -tohit, Defense and resistances will all be counted before absorb, there does come one additional question. Since Wild Bastion is on such a long recharge (240 seconds), how long does the absorption bubble last? Does it go beyond the 10.25 duration listed in mids? The question comes since the healing portion of WB last for that duration.
If that's the case, then adding res becomes way more important than adding HP. If not, then res still probably wins, but not by nearly as much since you still want to make sure you are not hit by enough to kill you and +HP has a universal flair since it has no damage type consideration.
Keep in mind we can't just jump onto test to confirm anything anymore, so I'm going from memory and my interpretation of the power definition. If my memory of absorb mechanics is correct, the correct way to read Wild Bastion's City of Data definition is that every player had an absorb bar, analogous to their health bar, but the max of that bar was normally zero. So when we say a player had "1000 health" what we really mean is that their max health was 1000, and of course during combat their actual health could be lower than that. Important to remember that in a sense, damage and heals were "permanent" in that normally they did not expire. If you were hit with 100 points of damage, that damage was permanent in that it could be healed, but that damage subtracted from your health and that was that. Similarly heals were also "permanent" - they had no duration, they just added to your health bar and that was that.
Absorb was like that as well: you had an absorb bar, and damage to that bar was "permanent" and "heals" to that bar were also permanent. So what Wild Bastion did was two things. First, it buffed your absorb bar
maximum to a level that was computed to be 25% of your health bar. If you had 1000 points of max health, you'd now have a 250 point absorb bar *maximum*. At this point, how much absorb do you have?
Zero. All that effect did was give you a 250 point absorb bar. Now, on top of that, Wild Bastion *also* gave you a "25% absorb heal" which in effect filled your absorb bar. So now you have a 250 point max absorb bar, and that bar contained 250 points of absorb. How long does it last? Well, the points last forever, or until you take damage. But the max absorb buff lasts only 60 seconds. When *that* expires, your absorb bar drops back down to zero max, and of course any points inside the bar disappear.
Think of it like Dull Pain. When you use Dull Pain, two things happen. First, DP buffs your max health by 40%. And then it also provides a 40% heal. So if you have a 1000 point health bar, then first that gets increased to 1400 - but your health is still 1000 points, so it actually looks like your health bar is only 71% full. Then you receive a 400 point heal, and that fills your health bar up to 1400, and your health bar looks full again. Those were two separate effects, and when you used DP you could actually see both effects visually affect your health bar. When DP expires, even if you have all 1400 points of health, when your health bar drops back down to 1000, you lose any points above that. Most absorb effects acted like DP: they granted you both an increased Absorb bar (typically increasing from zero) and some actual Absorb points to fill it. The points didn't expire, but the bar itself did.
Now, am I 100% certain that resistances affected incoming damage before hitting absorb? After all this time, no. I'm 95% certain. I'm 100% certain that if they did not, they would soon enough because in City of Heroes that kind of discrepancy between defense and resistance (defense obviously always protects absorb points due to the way CoH tohit mechanics work) tended to get nullified sooner or later. I'm pretty sure if I detected that difference in testing, I would have wrote it up and I don't recall doing that.