What a myopic question. There's 30 companies registered to do the annual backflow inspections that the city requires on my property. When I get the list, I don't think to myself "Man, there's at least 30 companies making buck inspecting people's pipes. I better start a backflow inspection company! How can I disrupt these people who've managed to scrape together some profit?"

Yes, yes - Slack gets all the news and chicks and is probably bigger. But it's the entire mindset. You wouldn't start an HVAC repair company after hearing that an HVAC repair company is doing well, even if they're the biggest one in the region and even if they're making millions; similarly, you shouldn't start a chat app just because you hear Fortune magazine writing about a chat app.

There's another part to this too: With the word 'disrupt' I'm hearing "Slack is doing well; I'm jealous of Slack; how can I hurt Slack?" I used to have a neighbor that would get jealous of people and key their car if it was nicer than his. Nobody liked him and eventually they arrested him for unrelated reasons.

Don't phrase your business plan as being the equivalent of keying Slack's car.