TDRL isn't terrible. It can go up or down, depends on the facts. The biggest problem with TDRL is they won't ask the VA for ratings and can come to some disappointing conclusions due to what can only be explained as a poor understanding of the VASRD. The easily solution to that is get a VA exam/rating before the TDRL eval. AF tends to do that anyway. The specific example you showed is not easily relatable to your case. The way I read it, they had not done much insulin therapy before discharge, so it makes complete sense that insulin would end up improving his case by the time TDRL eval came around. Your case should look considerably different as you have been on insulin for awhile.
I am curious why he believes you should look into TDRL. TDRL will give you a chance to argue for fit later down the road, under the assumption that you can more clearly show fit after years of being successful at managing the condition. Jason addressed this in your other thread about being a risky strategy. I don't see a good way to argue for both TDRL, which will require your condition to be rated 30%+, and fit. I think your best case for a fit finding is now, not later on TDRL.
However . . .
I commonly associate TDRL will MH conditions. I am wondering if the PEBLO isn't saying TDRL for a MH isn't a better route to go since it looks like the diabetes is unlikely to result in retirement or a fit finding. If he's trying to use short hand for go get depression or PTSD added as unfit its hard to disagree. Symptom exaggeration for MH tends to not be very successful, but I don't think that's really how it goes down. I think the majority who get MH conditions added on to their MEB aren't being dishonest, I think they finally decide its time to stop hiding symptoms and put their cards on the table. From the outside its impossible to say that would be the case, but if it is, it may have a better chance of reaching a decent end line, retirement, than arguing to stay in another 4 years. I can't say so much so that I'd recommend it, it sounds like you have a good case for fit, but I would be very worried if the case is good enough and may consider sucking it up and facing the shrinks to protect my retirement in your shoes. As you pointed out in other threads, its either fit or 20%, but that doesn't account for the 3rd possibility, adding more unfit conditions.