Haven't read all replies thoroughly, so in addition... or subtraction to them...
Firstly, from just a few pics & a little info, many things are unknown & can be misinterpretted, aside from differences of opinion & experience, so bear that in mind when reading/learning/asking. More pics and info would help if you want more specific opinions & doing some study for yourself into hoof health would help you & your horse.
It appears the soles are quit thin & 'dropped', at least in the front half of the foot and there is some separation & flaring. It also looks like the frogs aren't too bad, but have possibly recently come from 'bad' & that central sulcus may be harbouring thrush. With the toe wear & look of frogs, I'm guessing he's 'tippy toeing', perhaps because of heel sensitivity.
It's unclear to me, with these pics only & it being an older job, whether the trimmer has done a good or bad job. However, if the horse is always sore after a trim, while there can be exceptions, that generally means something may not be right with the trim. Be interested to know what they've said/advised? How often is the horse trimmed? I'd be inclined to trim little & often on these feet until they become healthy.
The horse could be in this shape due to his diet & environment, other factors that have led to laminitis, could be due solely to bad mechanics, etc. While trimming & supporting/protecting the feet adequately can go a long way, if the cause is laminitis or such, addressing the underlying cause is also vital.
I would not ask a horse in that state to work barefoot on hard/rough ground, as he won't be using & therefore developing health in his sensitive heels, and his thin soles leave him at risk of stone bruises, abscesses & worse. IOW, it's not even about 'transitioning' to bare, at least until you can get the feet healthy & functional first. As steel rims provide no protection or support to the underside of the foot, I'd go for hoof boots as a first choice or at least shoe with pads.
Leaving the sole weight bearing like that reduces circulation
IMO the sole & entire bottom of the foot is meant to bear weight - I don't believe god/mother nature would have put it there otherwise, for one. But it is all meant to *share* weight distribution and no area be under constant or excessive load. I think peripheral loading - forcing the walls to bear the entire load & leaving the underside without support is what can really effect circulation. So saying, as I said, the sole should be sharing, not taking the full brunt any more than the walls, and a sole in this condition, IMO is definitely needing padded support to bear the load without further damage, until (tightly connected) walls can share the job.
As far as the sole, what is to be done about that? I distinctly remember the trimmer saying that he doesn't like to trim the sole unless he has to. He wants the sole to wear off on its own. I mentioned something last time he was here about the big toe callous and he took it down a little bit. The trimmer didn't seem like he was too bothered by it.
I agree with the principle of not trimming sole unless absolutely necessary. That you commented on the 'toe callous' and your trimmer obligingly trimmed a bit rings loud warning bells to me. Like I said, from only a few pics & little info, could have a different idea about what is actual, but it appears that far from being calloused excess sole that can afford to be trimmed, there may be very little material covering a 'sunken', protruding pedal bone!
That he 'didn't seem concerned' is not necessarily an indication that he wasn't, and many farriers aren't very communicative with their owners, but I personally think it's vital to inform owners of the state of affairs as I see it. After all, you can only start helping your horse if you can learn what's what.
Hoofrehab.com is one good place you can start learning more.