Oftentimes I find medical research not interesting, most of the people that do strength training know the anxiolytic effect, there is no need for an nth paper to say it, there is a need for research that explain why it is true.

Meta-analysis help in showing trends, it's kinda valuable per se, but there are meta-analysis that show important things that were previously difficult to find because they were scattered in the literature, and the litterature was not with the same sample of people. Here the insights are pretty small, there was not really a doubt about the effect of strength training. A better analysis would be 'which people do not benefit for anxiolytic effects doing sport'. That's unknown, do these people even exist?