For one thing, its a game, okay? So it won't be totally realistic. And you could do the same kinds of leisurely activities in K2. In K2, the Sith never made any appearances until Korriban. In K1, you had the Sith fighting you on every planet, including the cutscenes which let you in on what Malak was doing, you had to go to their own planet, and you even had fighters chasing after you periodically whenever you left a planet. And of course, you ended up being caught by them at one time! Nothing of the sort in K2. You didn't even see them until the end, unless you did Korriban early.
The Sith in K1 were free to reveal themselves because Tatooine and Kashyyk were both planets outside of Jedi grasp. Jedi were needed elsewhere and so couldn't fight the Sith there even if they did know. And as for Manaan, it was a neutral world, so Jedi couldn't fight the Sith there either. In K2, the biggest threat to the galaxy seemed to be mercenaries, cause that's mostly what you fought.
You're completely misinterpreting Malak's last words. His thoughts weren't of blame or "whining", but of repentance and reflection. He was wondering what would have happened had he not chose that path. And even if it was of blame, he admits himself that he has to take responsibility for his own actions after you speak to him. Sion, for one, does a complete flip-flop by at first priding himself in NOT being Kreia's student and then being worried if she liked him or not. You want to talk about whining, there's some for you. As for Kreia, of course she wanted revenge. She felt betrayed by both the Jedi and the Sith and wanted to get back at them. It was because of this that she developed a hatred of the force and both light and darkside (even though she was evil) and wanted to blame the force for all evil in the universe. She wanted the Sith and Jedi to accept her views, but failed to realize that she was in fact wrong and her own views were self-defeating.
If you don't have those powers, then it's a little harder, isn't it? It took me a lot of trys to defeat Malak on my first playthrough. Sure, it got easy afterward, but I'm talking about initial playthough. In K2, I defeated Kreia in one try, and that's with a consular/Jedi Master build! If you have force immunity and an energy shield/energy resistance, then it's that much easier. As a guardian/weapon master, she can go down in a few slices.