You could use the entire network stack, sure, but that still isn't going to be very fast, since any app that uses the radio frequently is going to drain the battery, and users will complain, which mean such apps just don't exist.
You can settle for only getting an idea of how useful the network is once every 10 minutes, but then we're back at the problem of the "network quality" metric not actually meaning anything relevant.
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Since we already know that the mail client doesn't kill the battery dead, we can guess it's not checking for mail very often.
Sure enough, google tells us the most frequent check possible is 15 minutes: https://discussions.apple.com/thread/1596018?start=0&tst...
You could use the entire network stack, sure, but that still isn't going to be very fast, since any app that uses the radio frequently is going to drain the battery, and users will complain, which mean such apps just don't exist.
You can settle for only getting an idea of how useful the network is once every 10 minutes, but then we're back at the problem of the "network quality" metric not actually meaning anything relevant.