In defence of Hills I fed our boy what seems like every food under the sun (including raw - which made it worse) to try & control his skin problems - there is a long thread on here somewhere regarding it. You can buy over the counter Hills Skin food which was no-good. Whilst at the vets one day with our older dog I mentioned our problems with the boy & she suggested / not told to or sales talked us into it, suggested we try Hill D/D which is a prescription diet.

We changed him over 10 day period and we have never looked back. If it hadn't worked, Hills do another one called Z/D which has nothing in it that a dog could be allergic to. However the D/D suits. He gets a mix of (soaked) dry D/D kibble & wet (tinned) D/D

It's like everything else, what suits one dog doesn't suit
another.

I think listening to your vet is good and sensible BUT if you have done a lot of research an know the raw diet you feed is balanced then I would stick
With it and find a vet that will help not hinder.

One of my vets ( the nutritionist who stocks the food they sell) pulls a face when I mention it, our other, best vet in the whole wide world, trusts us to do the best for
OUR dogs and so is supportive as she knows how
Much research we do into any decision we make ( she is also supportive of us not vaccinating our older dog).

I agree dogs cannot access any enzymes in grass but long tough grass acts as an emetic/stomach irritatant to some dogs so there can be reasons to prevent them eating grass.

It can set up vomiting in some dogs and there can be good reasons for not wanting them to trigger this, such as wanting to rest their stomach during recovery from GI upsets, or if a dog has a sensitive stomach.

Yes it can be a normal behaviour for queasy dogs to attempt to purge themselves (and some dogs happily eat grass without vomiting), and generally they eat a little grass, vomit some bile and happily settle to eat but dogs do not always act in their own best interests! Some dogs who do not vomit back the grass can also have problems passing long stringy grass stalks at the other end.

All about people knowing their own dog and acting accordingly I guess.