This claim that system fonts are the "bottom of the barrel" is just so clearly false that I don't understand how you can be an advocate of typography and say it. Both Microsoft and Apple put huge amounts of effort into typography, contract or employ well-regarded designers, and their outputs are themselves well-regarded.
If you wanted to say "most of what's on Google Fonts is bottom of the barrel", you'd have a colorable argument. But that isn't what you said.
San Francisco is a great font. Arial is a perfectly functional semi-clone of Helvetica, Times New Roman is a decent interpretation of Plantin. Roboto is an interesting mash-up of Helvetica, DIN, and a few others.
System font from a web standpoint means you get one of these depending on the user's choice of phone, desktop, and/or browser.
It is somewhat like buying art because the frame covers a blemish on the wall. That the print inside the frame might be of a famous impressionist painting does not mean that the frame or the print necessarily go with the room.
The car analogy involves a car rental place - that they may give you any one of several newish, functional and even stylish vehicles does not change that you may often wind up being paired with a vehicle mismatched for your function.
Around the time Matthew Carter was creating Georgia, one of the most widely-used system fonts in the world, for Microsoft, he was also widely considered one of the best typographers in the world. Georgia is not hotel room wall art.
If you wanted to say "most of what's on Google Fonts is bottom of the barrel", you'd have a colorable argument. But that isn't what you said.