Buying of invaders is perfectly acceptable and often cheaper than fighting, although I admit I don't support it. You seem to be digressing into previous Kings here, this is supposed to be about the year 1066 after all. But I will answer this one anyway. Firstly, Harold showed plenty of balls in defending himself. He put his fleet (the best in europe at that time - thanks to Alfred) into the channel and only withdrew them due to attrition (I think we can all understand that one...). He reacted so fast to the Norwegain invasion he caught Hadrada completely unprepared. Next, he stormed south again to face William and in so doing was himself not fully prepared for battle (I shall explain further below answering another of your points). This does not show a 'lack of balls' perhaps you could explain why you think he did show a lack of balls. Furthermore, the Saxons did have some castles, it's a common misconception that they didn't. Castle building (in stone) was a new technology and even the Normans didn't have a large number of them although they were very quick to take it up. The Saxons also had a defensive network, the Burghs, these allowed for the intake of local population and goods in such an event (again I will explain further below). These were positioned so that no one was more than 50 miles from protection and I think show a major difference in thinking between Saxon and Norman. That is the Saxon wanted to protect the people as well as themselves, whereas the Normans were only interested in placing a statement of individual power on the landscape and protecting the themselves.
Apart of course from the repeated rebellions that dragged on for years...
As I said in my post beginning this thread 'if Harold had been more prepared' then yes he would have won, I have no doubt about that whatsoever (I shall expand below). And as I said above there was a defensive network. I don't see how you can claim the Saxons didn't move with the times, they were respected throughout Europe. They had the best infantry in Europe, the best fleet, European monarchs were sending their son's to the Saxon court to learn how it was done. Williams own advisors thought he was mad attempting an invasion because the Saxons were so feared!
OK. There are several contributing factors. The bulk of the Fyrd was left at Stamford Bridge, not a huge problem because he was gathering another to face William, but, he did not complete this task. So he only went to face William with his Huscarls and a Fyrd he had not yet completed and didn't know properly. The reason he did not complete the Fyrd is that William was goading him into presumptous action by burning the Godwins own villages. Harolds advisors warned him to wait but he didn't. We can only guess why he didn't but I would assume he was flushed with success after the slaughter at Stamford Bridge and angry with William for the burnings. I will freely admit here that Harold was wrong to do this, his ability as a commander failed at this point, but then hindsight is a wonderful thing...
Also by marching to face William instead of relying on the defensive network of burghs was a mistake. But you need to understand the Saxon mentality, when someone is burning villages, you attack them, you don't hide behind walls like a Norman. Also the lack of Cavalry, the Saxons did not fight on horseback, they considered it cowardly. Again I think this was a failing and contributed to their downfall. And finally the the lack of discipline in the new Fyrd (remember he had not had time to instill it yet) and the resulting attack downhill which of course has a famous outcome (whether it was Norman trickery or not). Had this not happened the Saxons could have held out long enough for the rest of the Fyrd to arrive and the Normans would have been finished. Instead of hating Harold for his failings I admire him for reacting the way he did because it proves he was a human being. I cannot however say the same for William. I also admire Hadrada for his failings that year, I think they were both true warrior kings, whereas William was to frightened to face Harold personally on the field despite claiming beforehand that he would...
