Firesign Define 'Limited' because looking at the above list, together with the Network connection, your 'limited' is actually all data from my Pixel phone is sent to Google.
You appear to be getting confused. The fact that 'Shell' has all these permissions does not mean that all data gated by these permissions is getting sent to Google. It is an open source system app that is part of GrapheneOS, not a proprietary Google black box.
Let me state again that all the connections that GrapheneOS makes and their purpose are carefully documented at https://grapheneos.org/faq#default-connections
Looking at system app permissions is not actually very useful and easily causes confusion. While some parts of the OS are system apps where you can view their permissions other parts are not - like the parts that create and enforce this permission model. It is pretty much an inherent property of any operating system that it has to have access to any data it handles and any network connections that it makes.
The GrapheneOS team have been discussing how we should deal with system apps and their permissions as it is a regular cause of confusion. Especially when people start denying permissions from system apps and later find some seemingly unconnected functionality on their device is broken. Its common for users to blame any breakage on OS updates, rather than considering that their own actions may have caused it. Over the years we have spent a lot of time diagnosing issues that have turned out to be caused by things like this.
Firesign Then one can assume some components are not isolated and can communicate with the hardware manufacturer.
By their very nature the cellular and wifi basebands are not isolated from the network and while technically they could connect directly to their manufacturers, whether that is considered Google, Samsung or Qualcomm, I am not aware of any indication that this is happening.
A modern smartphone is a very complex device. As a property of this complexity there are many potential ways that you could imagine that it could be technically possible for something to be malicious and be somehow exfiltrating your data.
It is however possible to examine the design, construction and functionality of software and hardware and to observe them during operation. This is constantly being done by many security and privacy researchers all around the world. The GrapheneOS team does this, as do many of our users and people we work with.
The fact that it it is open source, and in widespread global use, means that there are very many eyes upon the Android Open Source Project (AOSP). It is used as the base for far more devices than any other equivalent operating system code. The hugely diverse range of actors that somehow use the AOSP codebase acts to provide a collective guarantee that it behaves as expected.
We can not make 100% guarantees against every possible imagined security or privacy weakness. That is currently something of an unsolved problem and not really possible for any device, especially something as complex as a modern smart phone or personal computer. There is however a reason that GrapheneOS was built upon AOSP. It offers an unrivaled base when considering usability, security and privacy properties.