I mean, Elasticsearch does a whole lot of stuff, and I wouldn't expect a 'super light alternative' to do everything Elasticsearch does. If I were still dealing with ES, I'd look to see if it did the small section of stuff in my use case and if the API was reasonable and if it had a sensible operational profile and if it hit all those points, I'd try to use it, because I sure wasn't happy with ES.

Note that a reasonable API doesn't require it to match the ES API, and if I'm feeling really bitter, doesn't even include the ES API.

Now when someone says they're a replacement that's a lot more specific; I see ZincSearch makes a qualified claim of that form, if that's not accurate, then yeah, it's worth complaining. But lots of things are alternatives without being replacements (and really replacement doesn't always have such a narrow meaning either, kind of depends on usage)