Can you expand on why they think it is not good for long term soundness? I have not heard that before but would be curious to hear more about what they think on that.
Back to the OP - your most recent post suggests this horse is in the process of having his bad feet rehabbed - if so, the 4 week sounds much more reasonable, except, if he had really bad feet, he likely had very long toes and underrun heels, so the sole is probably very, very thin to begin with. The 4 week schedule is probably too much for him right now, since each successive cycle would set the toe back a bit more and put much more pressure on the walls and soles during rehab.
It may be better and easier on him to let him go 6-8 weeks between trims… and if he is really uncomfortable, get shoes on to elevate his sole from the ground, and the rim pads would help keep the sole from being bruised or having contact with the soil.
I’ve had good luck using rim-pads for one of my geldings, who has correct angles but given the nature of our turnout (he is on full T/O) which is rocky substrate/topsoil, he can shear off his hoof and sole quickly. The shoes + rim-pads were a good compromise - I had him in full pads for a while but disliked how his frogs looked after each successive trim, plus, he often would get dirt balled in between the pads and shoes.