Spine thickness vs. geometry thickness are two totally different things. The closer to the edge you get the greater the order of magnitude of influence the geometry has on cutting performance, so the thickness of the apex has the greatest influence by far, but...immediately behind it is also extremely important. Meanwhile, rigidity increases cubically with an increase in thickness but only linearly with an increase in width, so generally you'll want to increase the thickness rather than the width if you're trying to maximize rigidity while maintaining a thin cutting geometry, and so full flat grinds tend to do that best, allowing you to often have a knife that's thicker at the spine and thinner at the edge than many saber-ground knives. The main drawback that this can have is on the tang thickness and how that thickness and weight are managed. In general 1/4" thick knives tend to be not merely overkill, but a pretty absurd levels of overkill, and just amount to carrying more weight than needed, and often have a geometry that's thicker than needed as well. There are very few contexts where it's considered advantageous from an engineering standpoint, so while it's impossible to say that one configuration is inherently better than others in a universal sense due to a lack of context, it can be said that 1/4" thick knives are optimized choices only for a very narrow range of contexts of use, most of which involve using it in very non-knife-like ways, while those 3/32" to 5/32" at the spine are more likely to be an appropriate option for a much wider range of tasks and settings. But if your context of use really does call for 1/4" thick knives, then you're making the right choice for your context--it's just not a particularly common context.