Personally I've wanted a good podcast app on Android and the Google app ticked all the boxes. Maybe Google is successful because of good product design in this case. However, I do agree the overall size of Google's influence is of concern.
Google get all the metrics, particularly on popularity of podcast apps available in the Play store. When new features are added they can see the metrics on increase or decrease in uptake, etc.. If the top podcast apps are using Google for advertising then that's more useful data.
This surely means Google are in a position to eat any apps lunch if they choose to. If Google couldn't release a product and have that hit the top 3 [on Android] in a few months then they have some serious problems; they'd have to majorly mess up their design or functionality, by not bothering to look at the metrics.
Now of course Google might choose to make something "innovative", but at least as far as which functions to include, and what people using podcast apps like, they're starting with a major advantage.
That's because searching "podcasts" on the Play Store yields Google Podcasts as the first result, and AntennaPod (arguably the best app in the market) appears on the fifth row.