A US federal court held that typeface designs cannot be copyrighted in Eltra Corp. v. Ringer in 1978. Federal regulations made this explicit in 37 CFR 202.1(e) in 1992. The government's explanation here [1] makes it explicit that typefaces are not subject to copyright protection, while fonts can be copyrighted as computer software.
This sounds like a typeface is not copyrightable but only because the mechanism for protection is different (patent system). So by doing what the GP suggests you wouldn't be violating copyright, but you may be in violation of the design patent on the typeface?
I'm not sure how common design patents are though. Relative to copyright, patents are much shorter duration and much more expensive and time-consuming to get whereas copyrights just happen (though you may want to register for greater protection--but that's still cheap and easy.
Yeah, agreed that it seems unlikely to be a problem for most typefaces. I just think it's a bit misleading to suggest it's guaranteed to unburden the typeface of any and all 'intellectual property' protections ("In the US, you can literally go and vectorize any font in the world and do whatever you want with it").
And, of course, I can sue you for copying my typeface even if I'll probably lose in court and you probably don't want to spend at least 5 figures in lawyers to defend your open source typeface design.
There are. (With the caveat of look the same as some typeface. Not all the kerning and so forth may be identical.) Overpass is one example I'm familiar with off the top of my head but there are many. https://en.wikipedia.org/wiki/Overpass_(typeface) Arial, notably, is also similar to (though distinguishable from with some letterforms) Helvetica.
There are: for quite a famous example see Monotype's Arial which is effectively free for Windows/Office users and is mostly indistinguishable from Helvetica by people who are not typography experts.
Most free clones are not as good in various ways, and good clones that are charged for probably get earn their creators a letter from a foundry's legal team that makes them decide that the cost (time and money) of defending their position (even though they should eventually win) is not worth it.
[1] https://cdn.loc.gov/copyright/history/mls/ML-393.pdf