This is a fairly standard and well-accepted method for comparing typefaces. I disagree that it's obvious that your "eye is going to blend the two fonts into a single set of letters..."
Why should sans serifs designed for readability on small screens look the same? One can easily see why any two would be similar, but it's not true that all must be.
I don't think the JMD's intention was to say that San Francisco was based off Roboto. He was merely pointing out how similar they are, which makes sense given that they took inspiration from a couple of the same faces.
Furthermore, there wasn't any implication that Apple didn't put time and care into developing the San Francisco.
This is a fairly standard and well-accepted method for comparing typefaces. I disagree that it's obvious that your "eye is going to blend the two fonts into a single set of letters..."
Why should sans serifs designed for readability on small screens look the same? One can easily see why any two would be similar, but it's not true that all must be.
I don't think the JMD's intention was to say that San Francisco was based off Roboto. He was merely pointing out how similar they are, which makes sense given that they took inspiration from a couple of the same faces.
Furthermore, there wasn't any implication that Apple didn't put time and care into developing the San Francisco.