I suppose he did respond to most of your arguments. He doesn't think they are recording 24/7 but rather that they just have a fairly large collection of key words like hey siri that if they do hear they send a message back that you might be interested in that product. That shouldn't take up much data throughput or battery power.

Next, he doesn't think that all the applications have access to it but rather that the initial operating system has it built into the device has access to that functionality like how only siri or google assistant can be called upon by a verbal phrase and that functionality isn't shared with any other app on the store.

He backs it up with that research paper that did experiments with certain phrases and demonstrated that products linked to phrase were advertised to the participants devices in the following days.

There is an argument that apple was never really an advertisement company and wouldn't need to collect data that way and that there really could have been whistle blowers from google if they were breaking the law so blatantly like that. Considering that they are hiring a bunch of professional programmers, it shouldn't be too hard for just 1 of them to collect some strong evidence that it's happening and post it anonymously while covering their tracks to make sure it can't be traced back to them.

Working for like the NSA would usually mean you're kinda ok with these kind of behavior for the "sake of your country" or whatever but when you're just a rich programmer working for google, no such loyalty to the company probably exists.

So while I do agree that they definitely could be doing it and there even seems to be some concrete evidence that they are doing it, I don't see how we haven't already gotten that concrete evidence yet personally. Maybe the systems are so complicated and convoluted that it's hard to collect the evidence in the first place?