They are very comparable. Both round fruit, often cut into wedges, both can be used to obtain juice.

I think what they saying “don’t compare apples and oranges” is trying to convey is that we shouldn’t judge an orange by the standards we judge apples. It would be silly to eat an orange and complain that it wasn’t enough like an apple.

Apples and pears can *cross pollinate and can be grown on the same root stock.

“This orange isn’t nearly red or crunchy enough to be a good apple.”

I’ve always taken it to imply that at a certain number of differences, the comparison isn’t useful anymore, not that there are no avenues of comparison at all.

I tend to compare apples to carburetors.

One of them objectively tastes better.

I don’t know about you, but I sort all my fruit according to tanginess.