First, I do feel that a hoof care provider should be able to spot founder/laminitis in a heart beat, without x-rays! We can't tell you the extent of the damage, but we should see that there IS damage already there or is happening.
That being said, your first farrier should have caught the founder before pulling shoes, unless it's happened since the horse was in his new home. A new diet, stress, etc can all contribute to a laminitic attack.
Laminitis is the actual inflammation, founder is the separation of the hoof wall from the bone, and both can happen together, or independent of each other. Chronic laminitis causes a lot of horizontal ripples in the wall, not always enough to really cuase separation, necessarily, but it's painful. Founder can happen without inflammtion-such as with White Line Disease or poor trimming/shoeing.
The previous owner's farrier may not have told them the horse had founder issues. It's suprising how many foundered hroses I starte working on and the previous farrier would have never described them as such. These horses frequently have flared hooves (dished) or flat, thin, or even bulging soles and are often shod with bar shoes or pads because they are lame in plain shoes. So if anything, I'd blame farriers in this instance.
I would recommend having diagnotics done by a vet to see the extent of hte damage and to help your usual farrier devise a trimming method to get your horse sound quicker. A new hoof does have to grow down, but exercise is the quickest way, along with proper trimming and PROTECTION of the foot.
A foundered foot cannot be expected to just "toughen up" on the rocks. The hoof is compromised, and boots with pads should be used or keep the horse on soft, firm footing without rocks. The sole is too likely to bruise and abscess (which is not only painful but can cause major setbacks).
Metal shoes, (bars and pads included) do not help much. They suspend the hoof by the very structure tha is compromised, and often let the sole drop even farther. The rigid support of the bar shoe does not allow adequate the hoof to function properly, in spite of it's "Support", so avoid it.
There are new materials available to help a foundered horse recover quicker, and you should talk to your hoof care provider. Vets aren't always up to date on the latest tools, by the way. They are busy keeping up with whole body science, and hoof care providers are more apt to know about the latest stuff for hooves. I say this because I inform vets of new things all the time and they just can't keep up with the technology or have no experience with it like a farrier/trimmer would. Vets are great, but it takes the vet AND the hoof care provider working as a team.
I don't see this as a death sentence, just a set back. Best wishes for you and your horse.