I think a good counter-example is Uber, with a separate app for ordering rides (Uber) and for ordering food (Uber Eats). Both apps are still bolstering each other by the brand recognition.
Additionally, the apps could still cross-reference each other in a subtle way. E.g. maybe when you type a podcast name in the regular Spotify it could redirect you to the Spotify Podcast app. Just like the Uber app sometimes nudges you to also order food.
I do think you're right that more subtle nudges are probably fine. Some might begrudge them but such promotions are a lot more tolerable than directly pulling an entirely separate app into your existing app and then placing the newly imported bits in the spotlight.
I think there's huge pressure to "everything app" very disparate services. I've also noticed that Amazon now lets you pull up your Whole Foods code or pull up the Whole Foods storefront from the Amazon app.
My initial claim only works for Uber Eats. It can only be used for ordering food. There's a button to order a ride but it redirects to the Uber app.
But I believe you're right that initially they were more separate entities, but now it's kinda merged.
Honestly, I think this could go much better if they just organized their damn software better and not damage their music offering with forced podcasts. Many of us would probably stay loyal and use it for podcasts as well if they made the experience great instead of forced.
Can't tell you how many times I was able to directly prove a change lead to a bad user experience only to be met with "Yeah but the data shows..." by some corpo cock sleeve of a manager or team lead.
All these shithead corps are actively monitoring AND MODIFYING USER BEHAVIOR without understanding human psychology or behavior science, because "The data shows"
IMO nothing short of a complete revolt in whatever fucking form that looks like.
It's far from new behavior for Spotify, though. They've been constantly twiddling with UI, algorithms, etc trying to optimize for profit margins over user happiness for years at this point. Last I knew their entire engineering structure is optimized for that, with the desktop client for example being carved up into wholly separate iframe "islands" (complete with dependencies in duplicate, triplicate, etc) managed by different teams to allow A/B testing of each pane without communicating with the teams responsible for other panes.