Firstly, that article itself notes, some of those cases were likely not whistleblowers (they were just relaying government information to news agencies, and even if trying to be transparent I doubt they intended internal negotiations with North Korea and Iran to to transparent
while ongoing). Secondly, that's but one aspect of administration transparency, there are many to consider, such as how much other information was released, when it was released, and how complete it was. Looking at one metric, even if it's an important one, and using it as the sole basis for making that judgement, amounts to more of a PR move and clickbait headline than useful assessment.
That said, I agree, Obama didn't appear to run a very open administration. It appeared very secretive. Then again, the prosecuting of of people for leaked information rather than quiet pressure and sanctions is itself a form of transparency (it's also noted in that article that past presidents used many other techniques to pressure reporters instead of the legal system).
In the end, this is a complex enough topic that without a massive investment of time and effort, most arguments are going to have a hefty amount of opinion, making useful discussion hard. It doesn't help that we don't have an easy comparison with Trump's administration. In one respect, it's likely the most open administration there's ever been. I just don't think that's by design...
