GraphineOS constantly spoofs the device's MAC so that argument is not valid (I also don't know how a website based email client is getting your MAC). It's also extremely easy to spoof the device's name. The way they are getting that is simply your browser's User Agent, or if it's an app, your phones root properties. There may be some other identifying properties about the device they can collect though, I agree with you on that.
Also, I agree with your argument about phones being tracking devices. Anything with a radio that connects to cell towers is going to be logged and tracked in perfect detail.
Also, I agree with your argument about phones being tracking devices. Anything with a radio that connects to cell towers is going to be logged and tracked in perfect detail.