I'll re-iterate that I find your goal laudable, but in my opinion your means strike me as being "off", not because you're wrong, but because you're offering a single stand alone change to play, which is neither simple, nor stand alone.
Heroic, or Epic fantasy is great. . .and the prime rule, before even rule 0 "The GM is always right" is "The players will leave if the game is no fun".
Everyone agrees on that point, I suspect.
The counter opinions in this thread you are getting are "I've not found it necessary to us +600 or +2000 OBs to form opponents into challenges for my players, I've used other tricks to get to the same end."
To which you keep harping on a point that RMSS is an example of stifling the high end of epic play. . .to which I offer this point based on my experiences:
"If you use the heavier mechanical elements like super OB/DB and immunities to jack up the higher end, you tend to need to push the PCs up to that end also, then suddenly 1st level enemies are no longer threats at all."
Which might be the dividing line between "Standard" and "Epic". . . .in one, Goliath is a dumb ass for not being worried that kid with the sling will kill him, in the other, Goliath won't be hit by the sling stone, and even if it does, it'll bounce off without serious injury.
This is an implicit problem with OB inflation. . . .in that due to the fact OB parry DB only affects one target, OBs in ranges as high as those bandied about here blow through any passive DB the RAW allows for, so you run up on sledghammer-eggshell complications where anytime you're attacked by someone you didn't parry, you die. . .so you jack up the passive DBs to compensate (I've been down the super high end game road before). . .when you get a DB like 200 or 400. . ..David goes from a viable threat to a one in a million fluke.
This changes the tone of RAW RM, which is an environment where 20th level paladins need to worry about being killed by obnoxious drunks who pick fights in taverns, not because said drunks are likely to win in a stand up fight, but because the odds of them getting a nasty single attack in are high. . .especially if they attack the pally 2 or 3 vs 1.
The primary reason why is because passive DB is low, and thus a drunk with a 20 OB with Dagger can kill you at 20th level. . .if you have a 200 passive DB there's no need to draw your sword, you can slap the three drunks into submission. (Which is what many other games feel like to me).
Of course, in that game, Goliath guts David, unless we assume David had a 500 OB with his sling. (He did have God's blessing, so perhaps).
There's nothing wrong with going out on that Epic end of the spectrum. . .I've had loads of fun out there, but you're not advocating a broad spectrum answer here on how to make large creatures work in RM, you're advocating a narrow answer of how to make high level monsters that happen to be large work in an epic flavor RM game. The 500 OB is not "How to make large monsters work." I suspect, having been out to the end of play you're playing at, that man sized and small monsters have very high OBs and DBs also, in order to be challenging.
I'm not saying your way is wrong, I tried to walk away with the YMMV above, but what you're selling doesn't match the label of this thread. . .. I'm 100% behind you offering advice on high end epic games, you likely have more experience on that aspect than any other poster in this thread. . .but if a GM looking to tune up his monsters a bit reads this thread and jacks up that Hill Giant to 600 OB. . .it'll be a disaster, because just making that one change as a stand alone won't make that GMs game Epic in scale, it'll just make that one monster a holy terror all out of scale with the rest of what's going on.
I'm down with Epic, I'd even be happy to see published material intended for Epic, but Epic is a holistic thing, requiring a bunch of changes, tweaks and adjustments, and what you do to make your game work is neither simple nor easy, and I'm guessing it took a lot of work over a lot of years to get the mix right.
That being the point I'm trying to make, that it's not that simple, and that the mid-high three digit OBs are not a simple plug and play solution for a GM looking to upscale large monsters, and that the "Epic Solution" is a bit more involved than just OB tweaking, and that if you want to open a thread to give the whole picture of Epic and all the Tweaks needed to make it work I'm 100% behind it, but jacking large monsters to Epic in a non Epic game would create more problems than fun.
Being the party pooper and pointing that out is necessary, only because a lot of people come here looking for game tweaking advice. . .and just jumping that hill giant to 600 OB without the rest of the bag of Epic scale tweaks and changes is more likely to result in a TPK than any other possible result IMO.
I've loved your posts lately, but I feel like I need to point out that context problem, because your Great advice for GMs looking for an Epic game might be really bad advice to a GM just looking to make a single stand alone fix to a non Epic scale game.
Does that make sense?