I prefer the term mobile-computer because it's a more accurate description of what it is. "Smartphone" is a marketing-term that immediately limits users' perception around mobile-computers. Your post is a reflection of that.
One of the qualities of libre or libre-inspired -software is that it gives users complete control. That control is usually restricted behind technical knowledge though. Thankfully the developers of the Android port of i2pd (hosted on f-droid and github) have created a GUI where users can set limits arbitrarily. The user can even disable transit for their router, but this is parasitic and I encourage all operators to contribute what they can. The notion that you shouldn't run i2p, i2pd or other such software on a mobile-computer is... nonsensical when you take it out of the consumer-smartphone context.
Mobile-computers trend on being more energy-efficient with larger battery capacities over time. If we're to take your concerns about data and energy scarcity seriously we need to address the CPU-cycles and data that are forcefully wasted against the users' wishes. We should tell Google not to transmit any data from the mobile-computer that's related to ad-networks. We don't want that and it's a complete waste of CPU-cycles and scare data that users have to pay for. Likewise we will prohibit Google from transmitting ad related data to the mobile-computer. Imagine wasting wireless networks by transmitting ads in high-resolutions and wasting CPU-cycles to decode it!
The reality is this: mobile-computers are incredibly sophisticated and capable. When corporations abuse your mobile-resources it becomes the norm and is not even questioned. What I suggest is users take control over their property and use libre or libre-adjacent -software to redploy those otherwise stolen resources towards things you actually want. You may want a lot or a little. If you dream big pack a few batteries.
Google does not honour that flag that 'grants' permission to specific processes to be long lived. It will kill it.