When working a Case the ability to view related activities in the timeline is essential.

When working with other activities than Email e.g. Portal Comment you have to open the record to check if there is any attachment and view it through Notes displayed in Portal Comment timeline.

My suggestions is:

If customers enable an activity table for attachments they should be able to view thumbnails of the attachment and preview it from a related table, like on the Case timeline. This is currently how it works on the Email table.

The creation of a record in an attachment enabled activity should also feel like sending an Email. The adding of attachments through notes in a timeline is confusing for the workers. Out of the box Notes on a Case is for case notes.

But if you set up Portal Comments to be your activity to your Power Page, Notes is used for adding attachments too?

Not ok for us as a business. Using notes for case notes in one situation and using notes for attachments in another situation.