Yep, I was at a table that wanted to see how tough Lolth was, at level 22 - autowon initiative, buffed ~+9 to hit, -10 to her defenses, autoknocked her unconscious, flurry of CdGs and she never got off a single attack.
It's very possible to cope with the problem, though I don't consider the above entirely a feature
Yep, the trick is to have a few characters who focus; take both +4 to a defense feats in one defense, for instance, then Mantle of Unity (everyone uses highest defenses in the group). Adding another 7-9 on top of that (Valorous Charge is an easy example) or giving the enemies -4 or so to hit (my controller tended to prone, daze, -2 attack the board when I brought him out) is just further icing on the cake.
I'll say, you've got a bard. If he built his character differently, he could do what I describe.
Agreed that the buffs/debuffs are the bigger problem, though I'll note that it gives you strangely divergent play.
Lolth's guards, for instance, will end up harder to hit than her because people use the limited use powers on her. A group holding themselves back might even have to grind an average encounter down for a bit, while the "boss fight" is trivialized. Much like you saw.
I'd have been fine if the math from expertise/defense feats had been baked into the system (and maybe fix that your 3rd defense drops precipitously vs monster attacks over time), if the rest of the system were a little more reined in. For example, let's say you hit an average opponent of your level on a 6. That'd keep you at around 65% average for epic, with spikes to 40% to 20% for the bosses, which you could pull out limited resources to get back to 60-80% success rate.