Separate populations for multiple brands in one BU, or not?

Question

For example, an fashion company with 5 different sub brands in one BU.

All subscribers enter from Service Cloud into one master DE. Each brand has a column in this master DE indicating if the subscriber opted in for that brand. I cannot change this process, as its maintained by another team in a different region.

However, i can create a new DE and use automation studio to filter the subscribers into different tables if i want. But for now they all exist in one master DE.

Master DE:
Subscriberkey
EmailAddress
Brand1
Brand2
Brand3
Brand4
Brand5
...

Marketing activities are executed per brand, no campaigns are sent to multiple brands. Campaigns do not overlap.

Now i want to build a data model in Contact Builder using Attribute Groups, but I have doubts about if to create new populations or not.

Should i just create an attribute group and link the master DE to the default model? Doing this makes all subscribers from all brands part of the same model.

Or Should i create a different population for each brand and create a separate model per brand? If so, I have read the Salesforce recommendation to create up to 3 populations maximum?

Thanks!

Note:
Brand 1 has +1.500.000 subscribers
The other have way less, like below 200.000 each.

Answer 1

You should be fine keeping all the contacts in a single attribute group. This will make configuration of e.g. entry criteria and decision splits in Journey Builder easier, as you will always only need to check the same, single data extension.

This is valid regardless of the sendable data extensions only containing a brand specific subset of these contacts, as the relationship to an attribute group is mapped based on Contact Key.

The numbers I would not be worried about, as long as you have your Contact Key as your primary key in your data extension, as these fields are always indexed, improving the lookup speed of your records.