I feel like we've been here before, have we been here before? Whatever.
Just for some fun, since you're saying it should be possible to do the numbers that the sims says we can do, let's look at some World of Logs results on Ra-Den from a high-level rogue. (shouts out to Kym from Apophasis for being Rank 1 Rogue for all 3 specs on Ra-Den)
Here's the Subtlety log,
here's the Assassination log, and
here's the Combat log.
The only major difference between the three parses is that in the Combat log, Kym hit Blade Flurry for the "free" cleave damage. I'm also 99% sure that Ra-den doesn't have any damage-done or damage-taken buffs like Jin'rokh, Ji-kun and Primordius have, so there's no discrepancy with the kinds of buffs Kym could have.
Subtlety did 60M, Combat almost did 65M, and Assassination did 68M. The fight duration was 4:28 (Subtlety), 4:20 (Combat), and 4:30 (Assassination).
Between the three, Subtlety is the clear loser. Even though Subtlety has the most "cooldown uptime" (Find Weakness, AR/SB, and Vendetta are the three I'm looking at), and even though the Subtlety fight was barely shorter than the Assassination parse, it still lost.
Meanwhile, Combat (with 10 less seconds to the fight) pulled 4M more than Subtlety with 10 less seconds to the fight.
We can look at these logs all day and come up with reasons as to why Combat couldn't get an extra 3M damage out (SND uptime, not-optimal cooldown usage, etc.), but in all honesty, is there any gigantic problem with how Combat has been tuned when you're looking at these logs? No.
Based on these logs, is Combat bad? HELL NO.
Other point I'd like to bring up:
Pretty sure I just brought up a bunch of awesome parses, and it's clear proof that it has nothing to do with "Why can't anyone playing Combat pull as good of numbers as the sims say?!" It has ENTIRELY to do with the thing you're just brushing aside; you simply CAN'T hit the number of GCDs that the computer can. It has NOTHING to do with "Combat is bad" (that's the thread's title, after all), it has to do with poor Tier bonus design.
I'm gonna go now, since my brain is somewhat turning into mush.