LefoDpct I'd counter that one.
Android & iOS was built in a different time, they where built knowing the internet was a very hostile place.
Yes there is the cellular aspect which is usually a very weak part of a mobile phones security (Pixel 9 onwards and newer iPhones have addressed this somewhat with better modems and firmwares), but when you take the whole package into account, unless its an M series Mac, no desktop / laptop can come close to a mobile phone, and the Mac only comes close because its hardware is based on the hardware from the iPhone.
Google could massively improve Android security, likely beyond what the GOS team could, but they have millions of users to think of, GOS doesn't, so they can ramp the security up further because their end user is looking for it.
So yes, you are right about the network being a potential adversary, there is a much bigger attack surface on any laptop / desktop because they are more "open" than mobile, even GrapheneOS, and that makes a lot of attack surface because 99% of users don't know what they are doing, the GOS devs do.
Also, most OS is carrying tons of legacy code, which also causes a lot of issues.