I don't think the parent said that Siri wasn't bad, on the contrary it sounds like they agree.

Their point is that if Apple totally scraps the current, bad, product called "Siri" and replaces it with an entirely different, much better product that is also named "Siri" but shares nothing but the name, people's perceptions of the current bad Siri will taint their impressions of the new one.

It's pretty clear they tried their best to miss or reinterpret the points I made so they could talk about something else.