More information about text formats
In general there is often not enough attention paid to the difference of clinical and statistical significance. I do not understand, however, how the authors of the letter conclude that the clinical effect in CASTE-AF was "tiny".
The application of Cohen's d to a study with a discrete outcome is rather unusual. A more intuitive approach, if one is unfamilar with hazards, would be to use the relative risk as outcome measure. The risk of the primary outcome in the ablated group is 28.5%, the risk in the comparison group is 44.6%. The relative risk is 0.64. The absolute risk reduction is 16% and the number needed to treat is 6.25 (for three years). Not a tiny effect.