This is true; the two ways of eating are quite close.
I suppose the differences I would flag is that some carnivores restrict further than just vegetables, perhaps not having dairy - so no cheese, cream, and sometimes even butter. Some on keto use things like dark chocolate as a treat, and again, that’s pretty much out on carnivore.
The other aspect is that there seems to be a difference in approach when it comes to eating windows. On keto, an eating window and IF are reasonably encouraged - on carnivore, the dominant ideology is to eat when hungry.
I think also the food quantity can be a psychological shift. Lots of long term carnivores talk about consuming 2lbs of meat a day (1kg). I think that’s the bit where you see most push back - most new people are shocked by the amount of meat that others consume; I don’t ever recall eating 2lbs of meat on keto.
I think it all comes down to how you approach carnivore yourself - and similarly, how you approached keto. If your keto was predominantly comprised of meat and dairy with a small amount of vegetables and an even smaller amount of fruits, then there probably isn’t too much of a shift. If your keto was full of keto friendly desserts or keto breads in addition to the above, then you might notice more of a difference between the two ways of eating - particularly if you follow a strict carnivore plan.
As for Phinney, he raises some concerns here:
They predominantly seem to surround access to minerals that would’ve been found in traditional cultures by drinking broth or maybe eating organ meats that are no longer easily found (brain, perhaps).
The other aspect is possibly the protein intake, particularly if he’s dealing predominantly with patients with Type 2 Diabetes which adds another layer of complexity. (This is something I was always mindful of when listening to the dudes - their information was exceptional, but my personal circumstances were very different to theirs.)
Amber has a bit on her site about both of these things:
Shouldn’t I be limiting protein?
Most people don’t need to limit protein, because it is essentially self-limiting. As long as you are not averse to eating fat, you are very unlikely to overeat protein in an attempt to get enough calories. If you’re worried about the depth of ketosis, see the first question. Moreover, it turns out that most people can eat more protein than they think, and still be in ketosis. Some can eat more than twice the minimum before ketogenesis falls below the therapeutic range. When you eliminate all carbohydrate, your protein allowance increases. For every gram of carbohydrate you ate on a keto diet, you can eat two more grams of protein than you were eating before to get at most the same available glucose. An exception worth mentioning is that people with hyperinsulinemia, typically recovering type 2 diabetics, tend to have a higher blood sugar response and quicker reversal of ketosis in response to protein. If this is you, or you just have a more acute response for some other reason, you may decide to moderate protein intake. Nonetheless, it bears repeating that the benefits of a carnivorous diet do not appear to be directly dependent on ketone levels, but on eliminating plants.
and
First, there are several compelling anecdotes of long-term carnivores who appear to be in perfect health, and who do not eat any organs. I have to concede that this seems stable and safe for them.
On the other hand, everything I’ve learned about human evolution and human brains suggests that certain animal sourced nutrients were critical for the development of the brain on both ontogenetic and phylogentic scales. For example, DHA is necessary in high amounts for brain functioning. In the past, we probably got plenty of that from eating marrow and brains, or alternatively, cold water fish. I think a healthy diet would include these. My point still stands, though, that this is a concern only if you continue with the diet long term, and your needs may depend on your starting conditions.
The fact is that most low carb dieters are not eating organ meats either; not carefully ensuring that they get plenty of DHA, for example. If you find fault with a carnivorous diet on this basis, and don’t equally criticise a low carb diet, that’s selective enforcement of your principles.
Source: http://www.empiri.ca/p/eat-meat-not-too-little-mostly-fat.html