I think NBC got confused too. Sylar should have died when Hiro stabbed him, like he should have died when Parkmen shot him in the second episode (I don't know if he stopped those).
Well, think about it this way: Future Hiro's original timeline consisted of Future Hiro stabbing a ready-to-explode Sylar, but he regenerated, and the bomb went off. But because Future Hiro went back in time and said to Peter "Save the Cheerleader, Save the World," massive repercussions resulted: Claire didn't die, Sylar didn't gain regeneration, and now Peter is the bomb.
Something so minor caused a major shift and changed Future Hiro's timeline. That said, it's entirely possible that other things changed--for example, maybe Hiro never got around to stabbing Sylar, especially when you consider that now Peter is the bomb. We just don't know the details of the new alternate future that Future Hiro created, and you can't assume that the previous timeline's events are exactly replicated in the new timeline.
And Sylar used TK to stop Parkman's bullets.
Why didn't Parkmen (or anyone else) think it was wierd when Nathan was able to reach through the wall, or the fight? Or when Sylar dropped the illusion? Did none of them look behind them?
Meh. Parkman did give Nathan/Sylar a weird look, but he decided to focus on getting through the door to Hiro. Not surprising; he had a job to focus on, and was under pressure--if he didn't catch Hiro, his head would be on a platter. And by the time Sylar dropped his disguise, those ice/fire explosions probably knocked everyone out, including Parkman. Heck, the door practically blew off the hinges if Mohinder didn't try to stop it.
Why doesn't Hiro just go back 15 or so years and get rid of Sylar when he was weak?
Again, the general idea--which Future Hiro hinted at--is that you want to cause as little repercussions in the timeline as possible. Killing off Sylar that early would screw up lots of things; saving Claire would, hopefully, cause fewer ripples in the timeline. And as you can see, even something that minor drastically changed the future.
It's like the whole "why didn't the eagles fly Sauron's Ring over Middle Earth and just drop it into the Cracks of Doom instead of forcing Frodo to walk a thousand miles." >_> Just don't ask these kinds of questions, I guess.
Does anyone have a guess as to what Molly can do? The show said she was the only one who could stop Sylar, which I disagree with. Mohinder beat Sylar, twice, Bennet beat Sylar, Peter coud beat Sylar, The Hatian could beat him. Everyone is just too lazy to finish him.
Well, there's reasons for all those situations. Mohinder is just stupid in general, Bennet/The Haitian/Eden got the jump on Sylar after he was severely injured, Peter was pwnd with glass. . .and you have to admit, Sylar is a pretty successful serial killer. . .except he has a one-track mind, with his brain-eating and all, which led him to make a few mistakes. All killers do, eventually.