So go and invent a new game that is not as combat heavy as D&D - or a new low damage class that fulfils your class fantasy. Rogues and thieves have always been top tier martial damage dealers outside 2e (where they were simply useless). They just had to work for it a bit.
Except, they didn't. Even in 3.5 they weren't top tier DPR builds. They were good, but there were tons of things immune to SA damage, and without SA, rogues were mediocre at best. Also, let's not forget, full attack. So after you did your damage dealing, if enemy still stands, you are in world of pain with your d6+con hp. TBH, best dpr builds relied on multiclassing. Fighters, even with modicum of system mastery, can get those numbers uuup. They have tons of feats, you just need good ones. For fighter, that was always focus, specialization, power attack. Over sized weapons. It's been a while since i last played pure 3.5, but that's the gist. Or you can forgo direct damage and go for standard spiked chain trip fighter. Those are nasty.
Here I think you are absolutely 100% wrong. An assassin should 100% be able to kill single foes faster and more effectively than a warrior. It's their job.
They should, if they can catch their target unaware. But in fair 1v1 combat, not really. Assassin isn't someone who will stand and bang with his foe.
The problems the assassin has are in multi way brawls and when the enemy hits back. Warriors can take it as well as dish it out and are much better able to cope with chaos. An assassin in a brawl generally wants to run.
Yup. Assassin isn't there to stand and fight. Surprise, hit from the shadow, hide, maneuver. Use dirty tricks like poison etc.