Since the implementation of hero pools into the Overwatch League this season (and also in the game itself) it seems like there was no clear direction for how the heads behind the madness wanted them to play out. There have been numerous changes to hero pools since their inception and another change comes in once again. This time, though, these changes look more beneficial to the higher level of play than ever before.
Starting this week, hero pools will be determined by just the playtime within the Overwatch League. Before, two different hero pools were featured which included one for OWL and one for standard competitive matches. This caused a number of issues such as players unable to practice certain heroes because of them being out of rotation in ranked. The next evolution of hero pools featured a singular pool based on play rates from "high level" ranked matches and the Overwatch League. This didn't work out as well for a number of reasons.
Finally, a singular hero pool will be determined by play rates for the Overwatch League which is arguably the best direction for pools. On top of that, only matches with an average of 3,500+ SR (Masters and GM) will feature hero pools. Anything other than that will have the entire roster available to play. This doesn't affect lower levels of play much as they typically tend to play heroes they enjoy rather than what might be considered the "meta" at the moment.
It still isn't clear if hero pools is the right direction for the game overall. It's also been hard to determine if they are considering the lack of consistency present in how they have been implemented so far. If the current format of the hero pools remain for a bit, though it will be easier to actually determine if hero pools were ever right for Overwatch or not.
Source: Developer Update