I think they’re just saying that teams forces you into using a thread, and make a choice to create a new one if that’s what you want. In slack by default you’re writing a top level message (ie creating a new thread)
Indeed, never underestimate the power of defaults. There’s a tendency on HN to say “well, everyone should just use threads on Slack then.” There is, of course, a way Slack could make that happen: make it the default.
(For what it’s worth, I much prefer Slack for communicating, but when I have to find something, I wish I were looking for it in Teams.)
Pedantic perhaps but maybe it's worth pointing out that Teams doesn't force you to use a thread. It just makes it the obvious choice since each top level message has a reply button directly on it so it's a single step process. Also when we're talking about Teams there's a big distinction between a Teams/Teams/Channel vs a Teams/Chat which is its own annoyance. They don't even support the same formatting capabilities (e.g. markdown) which is weird.