Firstly I find it really difficult to read your posts - so hardly read first one, just that he was lame & then looked at pics. Made the effort with second but punctuation would really help your cause.
Few things that you said...
The vet has probably considered he is not *clinically* acutely laminitic. Doesnt mean he's not sub clinical tho. There are a fair few signs of laminitis aside from lame after trimming, which if this is a regular 'look' could well be only due to the trim... and trimming like that will also cause/contribute to laminitis. Dark yellow in the laminae, bumpy, bulging look to hoof wall, hairline angle, etc. The stretched frog, and how it 'melds' into the sole show it has been a prob long term...
But if this is a regular sort of trim, again, I'm not surprised he is lame & you should consider your trimming may be the reason for - or at least vast majority of reason for his lameness. This is doing him harm.
You should NOT NOT NOT be cutting into the sole with nippers!!! At all! Ever! He obviously has too little depth at the toe anyway so I'd probably not be touching it at all. Certainly wouldnt advise you touch it, when you have removed way more than just dead sole, let alone not just flake bits that will come off soon anyway. You need to first learn what dead, flake sole is, what might be best removed & what shouldn't be touched, before you pick up the tools.
If you're trimming frequently enough, you won't even need nippers anyway for the walls. But I saw you mentioned leaving walls as long as possible - that's another thing you shouldn't be doing. The walls should be short, in relation to the sole plane... assuming adequate sole that is. Which there is not, at the toe at least. The heel and bar walls have been left overgrown and bars at least need trimming, likely contributing to his discomfort. Heel walls can't say from those pics for sure but guessing they could/should be brought down a fair bit.
His weak heels & severe thrush will be likely causing discomfort too & that also needs to be managed and protected and supported. It may be that he won't be able to stand having his heels brought down as much as desirable for his natural balance because of this, but as heels should be lowered gradually, and you will need to pad his feet for some time anyway(& poss always pad the frogs), I'd probably aim to take them down significantly.
The second last sole shot shows exactly where you should almost never trim the sole in the front half of the foot(the clean, trimmed area). It shouldn't be pared, shouldn't be rasped into & absolutely shouldn't be cut into with nips! As well as showing the overgrown bars that have been left weight bearing.
Last 2 pics are different horse, sole shot shows nice, strong & healthy looking frog but also overtrimmed sole, & can't quite tell if hoof wall is visible or you have 'dubbed' it away. Last pic shows the foot has flaring all round.
So... get those feet padded & booted immediately, to prevent further damage. As said I'd treat her as an emergency acute laminitis horse, similar 1st aid.