Well, it ain't the scope - swapped in the one I recently took off a different gun, and same results from the Howa today at the range (I'd say worse even but once you're north of 3MOA it gets hard to tell). So.... off to wal-mart for some epoxy putty with me.
TL;DR - OP is dead on the money, bedding on these things is awful from the factory, absolutely awful.
Note: I have edited this to correct the talk-2-text weirdness from the original post and add some more color for anyone who looks this up in the future:
So, I think I figured out the fundamental problem with mine. That accubock thing or whatever they call it is misaligned between the front and rear shelf areas. The front shelf, that flat part right behind the lug, is not in line with where the Tang bolts up; so either the tang sits flat in the stock, or the front shelf sits flat in the stock - but both cannot sit flat at the same time without putting the action under significant strain/twist.
I bedded the barrel section just in front of the lug/under the chamber with JB WaterWeld (does not make for a pretty bedding job, but it gets er dun, and is stupid-easy to work with; even I can do it), using Hornady OneShot spray on case-lube for release agent. For the bedding I set the action lightly into the stock (barrel sitting proud on the putty blob), and tightened the rear action screw first, and then brought the front action screw down to press the barrel into the putty epoxy, looking up from the bottom side to confirm when the flat section behind the lug came up tight to the stock/shelf. I did it that way (tightening the tang first) so I should not have gotten any forward teeter effect. checked to confirm I had plenty of barrel channel clearance, and all looked good (barrel does want to sit a touch to the left side of the channel, but that's just cosmetic - there's plenty of clearance/sheet of paper slides freely).
Pull it out of the stock after 2 days (way longer than needed for the epoxy - it's dry enough to handle in about an hour or two - it was just 2 days before I got back around to it), and go to tighten the action back up. Just make sure everything sits good and clean, I tighten the front action screw first and torqued it to 33 in-lbs. If I did it right, the action will be fully supported between the shelf behind the recoil lug and the new bedding I put in just under the chamber, and even with the front screw under torque, the barrel will still free-float without the rear action screw in place. Barrel free floats as expected. Perfect!
I go to tighten the tang/rear action screw, and I can visibly see the tang moving downward close to 1/8th of an inch before it makes contact with the stock/gets tight... But the barrel doesn't move because I've locked the front of the action into the bedding and torqued it... Well, now... that can't be good, LOL. So, basically, once the rear shelf (area behind the recoil lug) is pulled in flat to the accublock up front, the tang sits near 1/8th of an inch high of the stock in the back. Easy fix - I'll bed the tang and this thing will be setup pretty much perfect.
Other notes - I also pulled the scope rail back off and looked at it, and since I remounted it, there is definite signs that it's been moving against the top of the action, so between that and the action under strain as described above, it's a wonder it shot as good as it did.
My working theory of my whole adventure is, when it left the factory from Howa, the rail was torqued up really good and tight to the action (it was, when I removed it, it took some good force to break the screws loose), and the action was not torqued very tight at all (it was not - I remember the 1st time I pulled it out of the stock, I'd ballpark the action screws at maybe 5 in-lbs of force to break them loose). Anyway, between very light action screw torque, and the structural geometry created by the rail that was on good and tight, all that prevented the action for being twisted because of the misaligned accublock thing I described above. I swapped over to the Talley rings at the same time I pulled it out of the stock for the first time, and it's shot like crap ever since.
Since I prefer the Talley rings anyway, I put them back on there. Just for grins I mounted the scope with the rear action screw completely out and I only tightened the cap rings on the scope lightly. Then when I torqued the rear action/tang screw, sure enough you can see the scope ring move in relation to the scope. That's a lot of pressure (in a bad way) that was being put on the action.
I bedded the tang over the weekend (took 2 layers of waterweld - I underestimated how deep it needed to be the first try). I'll let you guys know later this week if it suddenly shoots good again.