Lots of team features, but even for individuals it has things like thread merging, snooze, tracker blocking, alias support, email templates, etc etc. Huge boost for work email vs gmail.
Also, it's available only as a UI on top of your existing mail server, so super easy to migrate on/off and plays nicely with other tools & clients.
[0] It does a lot more than email, and for that reason may be worth $180 a year, but you present it as an alternative for email.
Fully agree it doesn't make sense if you're just sending & receiving a handful of emails a week (but in that case, why look past gmail at all).
For comparison: Superhuman costs $360/year, Spike costs $144/year, Front costs $228/year, etc etc. Some people pay for serious email tools.
One under-appreciated feature: commenting on emails is incredibly powerful.
Now when I use Gmail, I find myself wanting to comment "paid" on bills, or "waiting for Dianne to call back before I book the event".
It's one of those simple things that make your life so much easier: when your inbox acts as a de-facto to-do list, having the status and next steps clearly visible makes everything stress free.