This results in a room which doesn't follow the default permissions for other types of events as defined by the homeserver.

For example, on my homeserver the default permissions:

        "events": {
          "m.room.avatar": 50,
          "m.room.canonical_alias": 50,
          "m.room.encryption": 100,
          "m.room.history_visibility": 100,
          "m.room.name": 50,
          "m.room.power_levels": 100,
          "m.room.server_acl": 100,
          "m.room.tombstone": 100
        },

but with this change, its only

        "events": {
          "org.matrix.msc3401.call": 0,
          "org.matrix.msc3401.call.member": 0
        },

Maybe it would be better to create the room with default permissions, and then update them to include the call states afterwards?

it's weird since based on my reading of [powerLevelContentOverride] The power level content to override in the default power level event. This object is applied on top of the generated [m.room.power_levels] event content prior to it being sent to the room. Defaults to overriding nothing. i was thinking it only changes what is included in the override,

But it seems like there is some confusion about this anyways
matrix-org/matrix-spec#492

So i'll change it to a separate call later