HN user
Can you be more specific? I don't mind the accusation, but peope on the internet™ have often different expectations of what a software should or should not do. There is no such thing as the perfect product™. It is all about tradeoffs.
A host can also be a subdomain. I'm using Isso on my personal blog for reference: https://blog.posativ.org/. It works exact the same way as for a top-level domain.
You are not doing full-text search with bloom filters (unless you add all partial words to the filter), only word-search, which is imho the biggest disadvantage (e.g. typos in the index or on the client's side).
Not sure what you mean. Isso does not authorize authors, hence an author URL does not necessarily list comments actually posted by author xyz.