I don't get your point.
So you're saying that because you don't HAVE to use a headphone it only takes one device?
Most devices that incorporate voice chat don't require headphones. But people still use them. So you're creating a false equivalency.
Headsets are necessary for voice chat on consoles because controllers and systems don't have a microphone, thus a device is needed to use VOIP. At least on PC you could find a Laptop or monitor that has a built-in mic like mine does. Sony and Microsoft choose headsets because they allow for solo conversations. Nintendo's decision to use a phone? They historically preferred open mic solutions for voice chat, allowing everyone in a single room to listen and chat, and services like Discord proved phones can be decent open mics. And since everyone has a phone, there's no need to develop or include extra hardware to facilitate voice chat, when people already carry a device that can fill that role. It's not a perfect setup by any means, but you should understand the reasoning behind it.
The point is that you only need your phone with the app open to use voice chat on Switch. It's not that different from only needing a headset to chat on other consoles. Sure, getting a headset-like setup is a bit more fiddly on Switch, and something that should be addressed as I mentioned because it is an issue, but it's not some needlessly complicated disaster many feared it to be.