So, each tournament has, let’s say roughly 30 hours of encore presentations. With 4 tournaments a year, and 3 years of viewership (starting with Season 3, then watching seasons 4 and the current season 5), you’re looking at around 360 hours, or 1800 OWL tokens; 2400 tokens if we’re being generous with 40 hours per tournament. That’s still less than half of what you estimated for all 3 years, and this 5th season hasn’t even finished.
I was able to find a confirmation in early Season 4 of OWL via the Overwatch Streaming Rewards Guide thread, where they quoted the OWL website. Not entirely sure about Season 3 Encores (if those were available or not), but I recall it was pretty implicit that encores were put in place to allow other time zones to earn tokens/rewards.