Hi & welcome to the fray!
Firstly, learn as much as you can about healthy hoof form & function. Owners learning for themselves is so important for the best of our horses, not least because there is so much new information these days, and many farriers & vets can have some contradictory & outdated opinions that you'll need to weigh up, which is better than going on blind faith.(check out thread link in signature below, for somewhere to start). Next, if you want some specific opinions/critique, rather than just generalised comments, post hoof pics(check other link in signature for what's needed), and info on his diet, nutrition & management. You'd likely get more if you posted in the hoofcare part of the forum too - you can ask mods to move this thread there.
Now, general comments... Firstly, I wouldn't call what you've described 'no issues' at all. It sounds like he has rather significant issues actually. Yes, it is quite normal for horses to have a hard time bare on gravel... just like people do, if their feet aren't strong & healthy & well 'conditioned' to these surfaces. That he is also reluctant on hard flat ground such as concrete indicates a much bigger problem though. He could be laminitic &/or foundered, although who knows without more info. If he already had quite compromised feet and he was shod conventionally with rim shoes, that is likely to have further compromised his feet, and he may need some TLC for some time before his feet start to become healthy.
I would suggest, along with other measures, that you invest in a set of hoof boots, or otherwise pad his feet, to protect & support his feet & allow him to be comfortable until they can become stronger.