Elder Basilisk
Interesting assertion. It appears that 20th level characters may bear that out.
That's a relief. Not that you agree with me, actually (it would be a very boring world if everyone did), but I kept thinking that by posting "I don't believe you" I may have been offensive.
For the record, I didn't intend to be offensive, and I'm glad you didn't take offense.
IMO, multiple stacking empowers are only a problem if they're combined with some kind of improved metamagic ability. And, in that case, the problem is the improved metamagic not stacking empower.
We'll just have to agree to disagree then.
Hmm. BAB +15, +10 Str 30 (17+3 stat boosts, +6 enhancement, +4 rage), +5 weapon, +1 weapon focus, +1 bless or prayer = attack bonus of +32/+27/+22 which hits AC 44 on a 12 with the primary attack. Of course, what happens when he hits the unholy aura is another matter entirely.
My math may have been a bit off, too.

I think it was just a 50%+ chance to hit with the first blow.
PS a raging dwarven barbarian can easily ignore a DC 26 Fortitude save, such as that caused by
unholy aura used by a pit fiend. (There's also
greater dispelling, if you can target an invisible pit fiend.)
If the revised pit fiend is really CR 20, I guess I can buy that. I'll have to wait and see though. In most games I play in, our supposedly overpowered PCs wielding their supposedly broken spells still barely escape with their lives against half the things that are supposed to be challenging.
It seems our experiences are different. Perhaps your DM is more competent than myself, or perhaps he's out to get you?
Coyote
If all characters have to have that to compete, that means that a lot of interesting (but non-maximizing) options (in magic items, feats, etc.) will perforce be neglected. That's boring, IMO.
IMO, an opponent with weak hit points, such as a pit fiend, should be difficult in another way. (To whit - that crit alone took off a quarter of the pit fiend's hit points.

)
The characters I used were somewhat optimized, for 25th-level characters, although I come down hard on what I consider "cheese".
I wish I had a 20th-level duelist sitting around - I'd try him and tell you how it went. Better yet, a monk (he of the low offense).
IMHO a party doesn't actually
need those items to handle a pit fiend. This flying spellcasting creature rarely has a need to enter melee, regardless. (IME, limited as it is, the players did not "co-operate" with the tactics section, and I didn't expect them to do so, either. The pit fiend, which was powerful enough to cause a TPK, did get to kill the archer who was
held. That's the only time he took a full-round action in melee - and even then, he was invisible.
The high AC is nasty, but there are lots of ways around that, and spellcasters rarely need to worry about natural armor, in any event.