The argument is that the review process gets away with being crappy due to the monopoly position, not that it is leading to the monopoly. It’s a symptom, not a cause.
Also it’s possible that specific clauses in the guidelines are anti-competitive. Fir example a guideline that simply disallows any app that competes with one of Google’s Apps might be seen this way.
So those are coherent arguments I think, I just don’t agree with them. The Play Store is a google product, with features developed and maintained by a Google. Other stores exist that compete with it, with features developed by other companies. The reason customers went with Google Play is simply because it had momentum and scale, and customers don’t want multiple stores. They want one store with one set of rules where all the Apps are, that will be on their next phone. Customers benefit from a one stop shop.
If someone wanted to develop a better store, with libraries better than ‘play services’, what stops them? If you want to inter operate with and use the services of the Play Store, you need to make a deal with a google, and the terms of that deal are standardised by Google. There’s nothing obviously illegal or a abusive about any of that, as long as the contractual relationships are fairly administered under the law.