feat: make `vertical` output the default

[G-Rath]

I can't find anywhere that we actually said explicitly "yes let's make this the default", but I'm pretty sure that was the plan and we didn't say not to do it.

There was some discussion on #889 about this - I'm also pretty sure we were comfortable saying this isn't actually a breaking change, but since we've working on v2 it seems like a good time to change this all the same.