While there is some review for trusted testers, it's different than the public publishing. I don't know exactly how it's different because a) I can't publicly discuss the internals of the review process so b) I make a point of not learning too much in the first place lest I slip up.
To modify your second question, "why does trusted testers have any review?" Well, we're still distributing the extension, even if it's to a narrowly scoped group. As such, we don't want to, you know, send known malware to people. I honestly don't have a good bearing on how long tester review takes, so I'd love to hear more about your experiences.
Boy howdy, I don't want to touch the discrepancy between Google Play, Apple's App Store, and the Chrome Web Store with a 10 foot pole. Speaking 100% from a personal point of view, the only thing I'd point out is that it took years for those ecosystems to get good release tooling, and that was despite having significantly larger development communities and revenue impact on their respective companies.