Siri does more processing locally than Alexa does, but does upload to the cloud, and depends on the cloud, both for analyzing the statement and for accomplishing it. It can then execute local actions. The info uploaded to the cloud includes essentially all the relevant data for the query, so it doesn't particularly help with privacy -- it's just not the raw waveform.

But Siri sucks for MANY reasons, and not just technical ones. It does worse processing but also does worse cloud integration, and now vs. alexa, has a far worse ecosystem around it (alexa "skills" are pretty awesome, and trivial to create)

Pretty sure this isn't true. Siri won't work for me if I don't have an Internet connection.

That's not why people I know say Siri sucks: for us it's because it can't look up as much info as Amazon or Google. It understands the query, it just can't do as much with it.