It does feel generic. I'm actually retroactively impressed that the old one looked so classy using so many colors (pour one out for https://metalab.co, who is doing just fine). I actually loved the different treatments—the Slack brand always felt like one of their strongest assets. It looks like the Joomla logo now – https://www.joomla.org/
And I imagine it was also inspired by IRC channels.
> I'm reminded of the Philip Morris rebrand to Altria
IIRC that rebrand was done to distance the company from cancerous associations with the name "Philip Morris", whereas the only reason I can think of for Slack to do this now is to give them a quick short-term publicity boost to make them more relevant to "retail investors" -- that is, this corroborates rumors of a public offering later this year, and imho means that it's going to happen sooner rather than later.