Great question OP, because the environment is a huge factor. I trim a wide range of horses in a wide range of environs and certainly notice the difference. Of course trimming, exercise & diet are also important factors, and if other factors are well managed, horses can generally get by OK with some compromises....
My own horses.... when I was just learning about all this, I lived in the hills, with 40 acres of 'poor' sparse native pasture, rocky ground with 13 various & sundry equids on it(one was my donkey). Well I learned to trim my own, 'fixed' a few supposedly 'unfixable' & chronic issues and used to ride everyone barefoot, over many miles of rocky trails and gravel roads without issue. Took to looking after the other horses on the property - my friend's and a few neglected ones. Among the rest, we had a couple of tiny footed QH's & 2 flat footed TBs, one with a huge 'unfixable' quarter crack. They all came along well & all did fantastically bare. I thought I'd found all The Answers
Then I moved to a wet climate where my horses lived on lush, rich pasture which was waterlogged half the year. I also got pregnant and found little time to take them out of the paddock. Lo and behold, I found I lost The Answers!! I had underestimated the importance of diet & environment
. My horses ended up thrushy, occasionally laminitic & needed booting on all but soft ground.
Fast forward another 8 years or so & I'm in the same environment and situation as above, but they've been on a track set up for a few years now, so with restricted grazing & more movement. I also have areas of pea gravel where they hang out & where it's extra boggy. They still get very little out of paddock exercise(I thought now my kids are all at school....) but have been doing really well the past years, despite the tropical summer we've just had, where all manner of horses have been suffering laminitis, mudfever and chronic thrush galore! I currently need to boot them for rough terrain, but they're fine on normal road or trail rides.