Obviously I don't know anything about the job, or about usual council recruiting procedures.
But as someone who has done a lot of recruiting, if I had a pile of applications and one appeared with a 3 page essay attached that I was expected to wade through, I would be rolling my eyes and skim-reading if I'm perfectly honest.
Doesn't mean the person wouldn't be shortlisted, but it would be more of an uphill struggle than for someone else.
Obviously meeting the criteria is the most important thing. But rightly or wrongly, you can't ignore the fact that your application itself, the way it's presented and the way you have chosen to address the person spec, will have an influence, that's human nature.
For it to go to three pages, you must have addressed the person spec in some depth. That's what the interview is for. To get shortlisted you need to make it really easy for the recruiter to run down your application and put ticks in the boxes they have in front of them for meeting criteria. Then when you get to interview, you need to explain in detail and wow people.
That's generalising hugely obviously, more 'wowing' early on might be needed for some jobs and in some types of organisation. But by the sounds of things in your case, getting ticks in the boxes was important and although technically whoever read your application may have been able to tick all the boxes if they had time to read it all carefully and absorb it, there is a high chance that couldn't or didn't happen.
It's a learning point for you, and it's actually really positive, because it means (I expect) that there's nothing wrong with your skills or experience, so it's very easy to put right next time.