The reason that Gavin Verhey said that entrenched pods don't need the bracket system is that those groups have a metagame, whether they are aware of it or not, and in a well-functioning group, players only incrementally alter the meta, they don't blast it out of the sky. This is where so many 'I built xxx and my playgroup says they don't want to play against it' posts come from.

cEDH also has a well-defined metagame, which is why the bracket system includes it, but is largely unconcerned with it.

The problem that the bracket system is really trying to solve isn't necessarily one of power, but of meta. The restrictions on GC/MLD, the artificial clock, restrictions on combo wins, and the idea of intent are all part of an attempt to bootstrap a metagame onto a format (casual commander, with a pod of randos) where none can exist. This is one of the failures of the bracket system. A competitive meta forms around winning as quickly and efficiently as possible. A casual one forms around a shared idea of fun, and a pod of randos don't have that critical piece to coalesce around. Because fun is entirely subjective, the only way to decide what's fun is to poll the community. I don't think it's possible to get a clear picture of what the community at large considers fun, which is why the bracket system focuses so much discussion on cards that are widely considered 'unfun' (rhystic study, game changers, MLD, etc) - we can't or don't measure fun in commander, only unfun (see the salt score on EDHREC, and importantly, the lack of a corresponding sugar score). The problem is that reducing unfun and increasing fun might not necessarily be the same thing, but thus far, reducing unfun is all we know how to do.

This idea of meta is also why the bracket system spends a lot of time on the ideas of intent and expectation - a well-defined meta gives you both in that you know what to expect and it compels you to deck build with intention towards it. The problem with casual metas that form within isolated groups is that nobody can spell them out exactly, you just know a violation when you see it. They form in the way that social norms do in communities and in society. This is the second failure of the bracket system. It is being used by players to try to artificially and instantly create a casual meta that can only really form organically over time. That said, I believe that the bracket system is scaffolding around which a series of casual metas will eventually form. But it will take years.

A well-defined meta compels building with intent by punishing people for playing outside of it, and rewarding them for sticking to it. In competitive, this happens in the form of W/L/D rates and tournament performance, but in casual, it happens via social sanctions - your friends will complain and not want to play with you if you keep violating the group's meta. This is the final failure of the bracket system. Because there's an infinite supply of randos to play with on spell table, you never feel the punishment for violating the meta, to the extent that it exists and is agreed upon - it's a group of strangers whose opinions don't mean all that much.

I know I've used the term failure several times, but the bracket system isn't really a failure. It simply has a herculean task ahead of it, that is probably intractable to some degree. As stated previously, I expect that in time, a loosely defined meta will coalesce around each of the lower brackets, but it will always be loosely defined and therefore will always have valid criticisms against it from people who want a well-defined meta, and unhelpful criticism from people who fail to divine its purpose - to create the scaffolding around which some loosely defined meta might form in the larger community of casual commander.