Well if there is no "structural" difference, then I'm stumped. I've seen a barefoot horse with one front white and one black, trimmed by a fantastic farrier, wear his white foot down faster.
You need to consider every different factor - eg. High/low, previous damage, etc to be objective about it. Interesting point Trinity makes. I haven't noticed that personally, but different conditions make for different results. If white horn was weaker than black, then striped hooves would all crack down the 'fault lines' that would naturally occur.
I have tried to turn several horses barefoot. They got great feed, a farrier familiar with barefoot trimming, a pasture with hard rocky footing. 2 years of this and my mare still was sore when ridden often and wore her feet down to the sole.
Well first & foremost, as explained, keeping & working a horse bare in all situations is not suitable or realistic IMO. It depends on many factors & I NEVER said they 'should'. I believe hoof protection/support is needed for most horses in at least some situations we ask them to cope with.
Just because someone is 'familiar with barefoot trimming' doesn't mean they're good at it, or knowledgeable about the rest of the factors that effect the whole. If for eg. Your horses started off uncomfortable & were forced to work bare anyway, despite their feet not being in a position to do so, the damage done could well cause a lot more damage & prevent them from developing good function & strength. Again, I think horses should be provided with hoof protection/support if/when necessary, to allow them to exercise comfortably & without risk of damage to weak structures. To force a horse to work despite pain(whether feet or otherwise) is cruel IMO, not to mention not productive to long term soundness.
It depends on the environment & other factors IMO as to what 'ideal' hoof wall length may be for a particular horse, but generally, horses that live & work on hard ground *should* have walls that are trimmed/worn to around sole level, so perhaps it was also your perception of what 'too worn down' was that caused you to think they were wearing too much.
Shoeing came about because people felt their horses needed it, not because some one spontaneously said, "lets nail somthing onto my horses foot!"
Of course. And many hundreds of years ago, metal rims were the best they could come up with. These days though, we understand a lot more about the function of the hoof and have far better technology to provide other, IMO generally far better alternatives, in the form of hoof boots. Not that I think conventional shoes are necessarily bad, or that hoof boots are always the answer, just that they're generally the better option wherever possible, considering the health & soundness of the horse.
To Spirit, I haven't tried the new Trails on my own horses, but my clients that have bought them have been happy with them. Re velcro clogging up, periodically using a wire brush to clean it is effective.
Re soleguard, I haven't personally used it myself, partly because it's expensive, especially the special dispensers. I've heard it is awkward to use & often doesn't stay in bare feet so well, or hold up to very rough situations. I'm also wary of sealing up hooves for long periods when wet environment & thrush is an issue, tho I am aware of their 'CS' type being made to combat that. So, I think it's potentially a valid alternative in some situations, but it seems that boots are generally a better & more economical alternative. I'd be interested to hear from anyone who's had much experience with the stuff.