Harry's not 'weak' - he's just not as strong as the evil nasty things he faces.
Harry is also very young for a wizard in this universe. If you've read "Dead Beat" - you've seen more of Morgan, who is over 100, and the Merlin - whose age we don't know enough about to even fathom a guess, but he's old. Harry's a 'teenager' as far as his wizard powers go, and while he has a truckload of power (he's one of the 40 or 50 most powerful wizards in the world) he doesn't have the discipline to gain the proper control so that he can work things like Morgan does. Harry hasn't 'honed' his skills as well as he should and part of that could be because of his backstory.
Harry was raised by a dark wizard, taught by a dark wizard and we don't know what Justin taught him and how much, aside from the Laws of Magic, that Justin kept from him. Then, his father-figure turns out to be 'the bad guy' and he has to take him out and he's sent to stay with Ebenezer and he, essentially, has to start his training all over again.
First person - the fact that the story is told from Harry's POV is an important factor when looking at the mythology as a whole - and even just the story points. Harry's just one guy and when he goes to face a vampire or 12 or a demon tree at Wal-Mart, he's doing it on his own. He doesn't have a team to call in for back-up... not directly. Also, factor in his deep-rooted chivalrous streak and that makes for all kinds of weird things that pop into his head - he doesn't give people certain information b/c he feels he has a responsibility to make sure the wrong 'things' don't fall into the wrong hands, he protects people; he fights the good fight and gets smacked down for it at every turn by the likes of Morgan - the fact that he hasn't quit yet is astounding.
The first person thing also clues in to why the women are generally attractive -- how many 'averagely attractive' people do you remember who aren't your close friends? Harry *would* remember the 'hot demon chic' who almost took his head off a lot better than he'd remember the 'average looking woman' at the counter at the drug store - unless the average woman tried to take his head off too - then he'd remember her pretty well.
Though, I will step up and disagree that all the women are pretty - they're not. Susan, from Harry's POV is sexy and hot; Murphy he calls 'cute' - but never to her face; Charity (Michael's wife) is average, she's not unattractive, but she's not a super-model either. And, it is a distinct possibility that Harry subconsciously finds the beauty in people - he is rather prone to thinking people are inherently 'good' until they prove otherwise.
The man (Harry, that is) has problems left and right - this, however, is part of Jim Butcher's 'formula' for how things go for Harry - (the following is Jim's reply to a question from someone on the McAnally's mailing list:
Well, it's really all about adding that one extra straw to the proverbial camel's back -- insult to injury. For instance, in Storm Front, it's not bad enough that a demon shows up to kill him. It's not bad enough that Susan is there too. It's not bad enough that she gets the wrong potion and transforms into a mindless lustbunny while he's trying to save both their lives. He's got to handle it all while naked, unprepared and with shampoo dripping into his eyes. THEN it's bad enough. I try to do most of Harry's crisis situations in much the same way, cause I'm gleefully sadistic when it comes to my protagonists in general.
It's just the way the stories work.
Also - (and this is getting really long, so I'm gonna stop soon, honest) - the books are only a few days in Harry's life. There's all that space between them where we don't see what he's up to - finding lost car keys, rescuing babies from trolls - where he could be finding the 'ugly' people and not getting his ass handed to him by the local demon from the sewer.
(( Jim's also mentioned that to grab the female portion of his audience, he has to include additional 'emotional' bits from Harry - which isn't sexist, so much as marketing. *g* ))
