I don't think the Villa game is a good example to use for any purpose as we were down to 10 men. I think if you want to blame Redknapp for the Villa game you're better off going down the route of why on earth haven't we signed a left back to at compete with Ekotto for the position, if not replace him as first choice. Same with Lennon on the right. By not having a ready made replacement for Lennon, we often had to go to this non-existant Plan B and that is what cost us.
I've been doing some analysis on our bad run of results (I still refuse to say form, because I don't believe we were playing that badly during the run) and for me there were three contributing factors that trump everything else:
1) Lennon gets injured we lose all shape and have to fit square pegs into round holes to accomodate. This completely ruined our attacking shape and made it harder to hit teams on the break, or break them down when they were playing deep.
2) During this period Bale developed a hero complex. Bale roaming around all over the place is fine if Lennon is staying wide and giving us width but when Lennon was out we had no width that side and then Bale would come in too tight and we'd have no width that side either. We effectively started playing a diamond formation which no one has really got to work successfully in the Premiership (cost Ancelotti his job at Chelsea!).
3) For some bizarre reason Redknapp dropped Dawson in favour of Kaboul when Dawson was playing superbly. Then Dawson got injured and defensively from set pieces we fell to bits.