You can put over 500 people Mattermost for $5/mo. And it's easy to get tightly integrated to your corporate environment - and even allow clients as temp-guest accounts for support.

Coding the custom solution around Mattermost cost less than one year of Slack and in year three we're still happy with it

Completely agree -- Mattermost is a great option for anyone. I'm shocked more people haven't adopted it. People need to get real. Slack is absolutely bonkers expensive. It may be the case that SV companies are happy to pay this price but you'll limit your market to SV. Slack is definitely finding it harder to grow -- they'll end up like DropBox.

2020 and 3 of top 5 economies in the world are Asian and you are still saying developed vs undeveloped countries. Update your biases please.

Is that because the asian countries are undeveloped and it therefore wouldn't be an biased thing to say? Its not clear what point you are making to me.