While I agree with sone of your points, there are many evidences that this happened in the past.

One example is Microsoft creating teams to take on Slack.

Teams is still nowhere near Slack's features and usefulness. I wouldn't say it's a direct competitor, it's like store brand vs a mid-luxury item

I dont think the founders or early team at slack are upset with how things played out

Every single org I’ve seen using teams (sample size of 4-5 orgs) uses it because it came for free. And every one of them also got slack and paid for it.

That says everything about how shitty Teams STILL is. MS still hasn’t improved it much from the steady state turd that it’s been a few years ago.

If, knowing what you know now, you could go back in time and be the one to create Slack would you not do it? Even if everyone is using Teams now (they're not), it took a really long time to show up that Slack's founders were able to capitalize on.

The change in the software landscape today is the apparent ability to develop a competitor faster thanks to LLMs. But, as the parent points out, the bottleneck was never code writing. It was waiting on the people involved to get past their egos. LLMs have done nothing to change that.