This isn't a particularly strong argument. Kleenex isn't on the antitrust chopping block even though you never hear anyone say, "Hey, can you pass me an AngelSoft?"

Even if that is true, do you deny that they are search engines themselves.

Siri, Alexa etc are even more opaque as they don't give a list of results, rather have deep integration to their own services and can't even be replaced by an alternative.