The problem with all the 'scientific tests' so far was that all the ones I've seen were severely flawed... to the point that their results become meaningless. Sample size too small, assuming 'factory knives' have perfect equal sharpness, only focusing on slicing vs chopping action. ATK literally has the robot cutting in the exact same spot for the entire test length. It should be possible to test this properly, in a way that reflects actual home or pro usage, but as of yet no one I've seen has
actually done this.
It doesn't help that places like ATK have a reference for sharpness that's basically 'running a Victorinox through an electric sharpener'.
It's also possible that there's an interaction effect where it will show up more or less depending on species (for example depending on silicate content). All of my experience is on European beech wood... where even just the cutting feel is
very different. Edge-grain vs end-grain beech wood the cutting feedback changes drastically, and for the better - though I won't speculate on the mechanics. But it makes it hard to go along with 'there is absolutely no difference' when the feel and sound alone changes so much.
Agreed, you also see far less damage on an end-grain board but for me - putting retention aside for a moment - the difference in cutting feel is enough to make it worth it.These days my knife usage is too eratic / spread out over too many knives it say anything sensible about edge retention anymore, but at the time when I made the switch the difference was noticable enough to make it difficult to write it off as entirely placebo (especially since the end-grain board was cheap).
I agree with you that hardness and silicate levels can also wreak havoc on your edges. Using a bamboo board for my bread knife was a really bad call... and after they started to feel and sound like 'scraping with sand' I've also lost a lot of my enthusiasm for even bamboo utensils.
Regarding hardness I've seen 'sweetspot' janka scale numbers floating around in the past.
But as a European it's really easy; go for beech wood; it's been the OG standard for a reason...and it's actually the affordable option too!