Bun and Deno are in totally different spaces to Boa IMO. Looks like Boa is comparable to QuickJS in the small embedded engine space.
QuickJS/QuickJS-NG might be a better comparison, but I think they are limited in specification conformance or at least selective in specification conformance in favor of remaining in a single file and fast. For instance, I'm not entirely sure whether they will be supporting Temporal once it goes Stage 4 because of the size of the feature, and I don't think they support Intl. But I also can't speak for QuickJS.