I actually agree with you that his impact isn't immediate.
But if you think any manager coming into this team will sort the utter mess out straight away then, to put it simply, you're wrong.
Mate, remove yourself emotionally from this and look at it objectively, you know our fans you know Goodison, what happens if we go the next 8 with 1 win and a draw, including a hammering at the pit, which given allardyce record initially at clubs is likely? He has once before worked at a place that went absolutely toxic on him - at Newcastle and they sacked him because their results got so bad they make our current form look positive.
I don't think any manager would instantly fix us mate, i'm not stupid, i think any manager coming in will need to do some serious adding in a couple of key positions in January - and i think that we need the injured players back - BUT i think many managers can do that in January, best we could hope for is a new manager bounce which gets a couple of decent results before the gashness of the team reasserts itself - we won't get a new bounce with Allrdyce - it's also something he doesn't ever give a team.
Will guarantee that a huge amount of the people calling for Allardyce will be already calling for his head come January if we go 4 points out of the next 8 games.