Sous vide: why do cylindrical / cylinder-like and spherical / sphere-like foods cook faster than slab-like?
A picture really helps here:



There's your slab, cylinder, and sphere with the same thickness.

The time to cook does depend on thickness, since that's the distance the heat has to travel from the surface to the interior. But it also depends on the ratio of surface area to volume (and thus shape): the more surface area per volume you have, the more area you have to transfer heat compared to the amount of heat you need to transfer to fully heat the meat.

So unsurprisingly, at constant thickness, a slab takes longer than a cylinder, which takes longer than a sphere.

Of course, the typical thicknesses of the various shapes are different, so it's not all that meaningful to compare things at constant thickness. A slab might be a fish filet, a steak steak, or many smaller pieces of meat packaged together in a bag - nothing all that thick, unless it's a really full bag. A cylinder might be a pork tenderloin or a decent approximation of a chicken breast - still not that thick. A sphere might be a single steak medallion, or maybe an okay approximation of a large pork shoulder - a pretty wide range.

That said, in the end we often think about things in terms of the amount of meat, i.e. the volume.  A 2 by 10 by 10 cm slab, a 5 cm diameter 10 cm long cylinder, and a 7.25 cm radius sphere all have about the same volume. According to that table, the slab needs 1.25 hours, the cylinder needs 2.75 hours, and the sphere needs 4 hours. So if you were thinking of similar quantities of meat, perhaps that matches your intuition better.