This is false. JSON allows both block and flow style. In fact, the JSON everyone is familiar with is flow style:
{
element: {
subelement: [1, 2]
}
}
The above is JSON and it is flow style. When Obsidian mangles it, it turns into:
element:
subelement:
- 1
- 2
That is not a familiar JSON format, and it is block style.
What makes you suggest that the frontmatter YAML (flow or block style) is converted internally to JSON (that is generally flow style) and therefore when it is written to YAML it has to become block-style? If this is genuinely the implementation the Obsidian team went with, it’s a terrible implementation.