I didn't say irresponsibly boosting the "to hit" of monsters was the best way to balance this. I said "buffing" the monsters is the best way. "Buffing" can happen in many different ways.
Here are some things I would consider to fix some of these imbalances:
1) Greensteel weapons are overpowered, especially the mineral II and the Lightning ones.
SOLUTION: The next end boss is immune to acid and lightning. He has regen that is slowed 25% for 6 seconds whenever he is hit by fire. Another 25% for cold, and another 25% for good. Plus, he's Chaotic Neutral. So Holy doesn't work. You want Axiomatic or one of the less popular greensteel builds for this one. Sounds similar to the hydra boss players have been hoping to see some day.
2) Wounding of Puncturing is too good relative to other weapons, so people who have it are overpowered. And, monsters have insanely high HP to balance out previous character buffs.
SOLUTION: Give a few new monsters deathward and reasonable (lower) hit points. But also give them 100% Fort and 30 point resist to fire and cold. Let them randomly cast other elemental resist and protection. Then use those monsters liberally in the next few quests. Puncturing and wounding go off even if a target has 100% fort and pretty sure deathward does not prevent con death. A_D has proposed a system in the past similar to something where mobs get % resistance to critical procs. That would slow and reduce the power of WOP.
3) AC is nearly meaningless in several important places because the monster's "to hit" is so high.
SOLUTION: Give players a way to get higher ACs a lot easier than it is now.
(Oh wait... they just did this with the Monk.) Actually they need to standardize AC so most characters are falling within a 30 point spread, vs the 60 point spread where only 20 points less then the max is even worth while to have, and give mobs increasing attack bonuses like we have with lower starting to-hit values. That way mobs are only likely to hit high ac characters with the last two hits while lower AC characters, within the spread, have a chance of being missed on the first two.
4) Giving players the higher AC made them too uber.
SOLUTION: Give some new monsters or end bosses maladroit of bone breaking. But make the monsters relatively weak, but put them in large packs. There is a 20 on every die, so a large pack means hits will get through. This will take down the dex and could also disable two-weapon feats on the people most in need of "nerfing" I would be in favor of giving boss and mini boss mobs access to either the prefix or suffix stat damaging weapons but not both together. The people you think are most in need of nerfing do not have to meet the min-recs for the two weapon fighting lines and so far no amount of stat damage turns off feats unless that stat damage kills you which would be similar to turning the feat off in an odd way.
Of course, deathward would protect from this and is very common. So make a couple of named bosses in the new quests have an improved version of this that penetrates deathward. Or, add casters or beholders to the mix so deathward will occasionally get debuffed.
I'm not saying all of the above are great ideas. But they are just the first thoughts that come after spending only seconds thinking about this. Clearly a design team at Turbine should be able to think of 50 other ways to balance this without nerfing monks.