Lync was completely unrelated software with a different tech stack that was just branded as Skype.
I know Teams is fairly pervasive, but that's on the usual Microsoft Enterprise stranglehold, certainly not on Teams' merits or riding the popularity of Skype pre Microsoft.
Also, even if you just want to buy Teams, from what I've checked the barebones Teams only packages MS sells for smaller orgs are still cheaper than Slack. Actually, let's see... yeap, Slack Pro's 8€/mo/user, Teams Essentials is 4€/user/mo, M365 Business Basic is 6€/user/mo.
I don't remember the last time I had a meeting on teams that didn't include a rant about teams