Just look at Rotten Tomatoes as the way the U.S. looks at things. Anything under 60% or under 6/10 is a failure and represents just degrees of failure. Because basically... if your product gets as many things wrong as it does right... it does not pass muster.
RT is really more of a two point system, fresh and rotten. They do their own thing.
If you look at Metacritic (a US site), they lay out a direct translation of out of 100 to grades:https://www.metacritic.com/about-metascores
Did you listen to the podcast? The ten point system is different for us in the USA. Anything less than 7/10 is garbage, if I got a 6/10 (D) on a school paper I would be grounded as a kid
5/10 is a straight up failure.
That's the thing, it's not, regardless of region. This is conflating grading scale with rating scale. Though it is right on the borderline. I've looked, and have yet to see any rating site that uses out of 10 that considers 5 to be a flat-out failure, hence why I corrected myself. My concession was that being completely middle of the road could easily be considered a failure to many.
But find me any site that uses out of 10 scale which specifically lists 5 as a failure rather than smack dab in the middle, I haven't found one. But really this isn't that big of a discrepancy, just a perspective at where true bad begins, at 4, or at 5. If something is given a 4 or a 5 by the majority of critics and audiences, I don't think it can be described as liked in either case.
And with 5 stars (how we used to do things around here), if you're going with half stars, it's really just another 10 scale system.