Rama, apples and oranges.
Discovery would have to be compared to other premiere digital TV (first run) series on CBS All Access (opposed to reruns of Matlock)... Which there will not be?
CBSAA doesn't have original content by the score yet, so yes Discovery is very likely to be the most downloaded NEW show (from that day or week) because it is the only new show on All Access that week.
Putting episodes on Itunes, seems like a violation of the exclusivity that Netflix bought for itself.
So yes, on a framework like Netflix or itunes, it would be a horse race... But unless there is a massive paradigm shift approaching, that is not what this is.
(The Good Fight finishes next week, and Big Brother 18 finished months ago, and Wikipedia says they have nothing else new on the table.)
Streaming doesn't work like that.
They get money from subscriptions and page clicks (6 dollars for advertising based All Access, $10 for no ads.), so what they want is perhaps in the shape of three obvious positive outcomes...
1. Some one watches all of Discovery.
2. Someone watches all of Discovery so slowly that they have renew their subscription several time to finish it.
3. Someone watches Discovery, and then feels compelled to spend a year, renewing their subscription over and over again, to watch the back catalogue of old Star Trek.