It's an MI5/Rupert Murdoch conspiracy.
No, its the 'new style' policing.
You do have a point about the idea of marching everyone to a single location: having four marches was a kind of riff off of J18, but the whole point back then was that they all started at Liverpool Street and headed off in *different* directions making it impossible for the police to pre-position themselves and prepare.
They all ended up eventually at the same place which was kept secret beforehand. While that location was, like most of the City, narrow, it had various alleyways and the layout made it far hard than the BoE to surround (they never managed to).
The fact that this Chris Knight character seems to have been somehow involved with this decision/planning, also with the talking-up of violence beforehand (even if he was trying to be "funny"), and with the Alternative Summit which was cancelled at the last minute with no alternative venue in place (and the original venue being a bad place anyway)... plus his fairly micky-mouse presentation and politics ... it does make you wonder if someone either put him up to it, or if his group got a whole bunch of mysterious assistance, funding, suggestions/ideas, volunteers and media coverage from the 'powers that be' (whichever branch takes your fancy) precisely because it was so crap (ie easy to deal with). However it is easier to identify this (people were saying similar things last week) than it is to mobilise an alternative late in the day.
It could be argued that having lots of small groups doing things throughout the City would be far harder for the police to prevent, and would have disrupted the City even more as the police chased anyone and everyone around the place and tried to shut down everywhere, potentially causing chaos. However it is only a small minority of people who ever turn up in small groups with specific plans and most people just want and/or need a simple 'plan' (ie meet @ location A @ time X). Being in a large crowd with a common aim, being able to see everyone, and the banners and music and performers etc, listen to people speak, do a bit of shouting, wave your signs around, meet your mates, have a picnic ... get some TV media coverage, then go home: this is what most people want to achieve. Yes you could cause a lot more chaos if the city was full of roaming bands of people hell-bent on smashing and looting and beating up anyone they didn't like, but that isn't what most people actually want to do or believe in doing.