Then slack is for both, because it has video.

But it's not really. It's primarily focused around text, and chime is around videos and meetings. That's the use case. Chime is built around meetings. Slack is built around chat.

This is not true. We use Chime for text every day. It doesn't have all the 3rd party integrations that Slack does, but it give you the same basic functionality.

Disclaimer: Work for AWS.

I use Chime in CDO ;)

Chime is definitely better than Lync, but I stand by my statement that it's not very good at text. It's missing basic UI features like threading or merged comments, profile pictures/icons, not to mention more advanced integrations.

I love using it for meetings... but text functionality is still lagging behind Slack, or even Mattermost (also used within Amzn)

It's definitely true. My team also uses Chime for text every day. The client has virtually no options, even basic formatting stuff that has been available on dozens of IRC clients for decades.

Disclaimer: Also work for AWS.

You mean it's not very good at emojis, bot integration, and other fun features that exist with other platforms.