I can't possibly see this going well for salesforce. Buying slack for 70x revenue is insane. Their entire market is going to be eaten by teams and google chat, if it hasn't already. Microsoft has such a gigantic advantage when it comes to enterprise productivity software because everyone is already using office. And those that aren't are on g-suite. Slack's recent guidance was horrible too.
Google chat isn't a real competitor in the space. It has always been Slack and MS, and being #2 is a rapidly growing sector is still very valuable.
A company that uses G Suite certainly isn't going to use MS, and usually won't choose to pay separately for Slack.
In what sense therefore could it possibly not be a real competitor? It's there, it works, it's fine. It's also relatively young and so we can expect it to improve significantly over the coming years, similar to how Meet has been improving over the past few years.