Yes, but most people don’t reduce broccoli or cauliflower to a sauce. Well, not commercially, anyway 
Also, in comparison to the other two listed, tomatoes are significantly lower in protein and somewhat lower in fat, as well, making the carb percentage higher.
I’m certainly not saying don’t eat them, just saying to keep an eye on them. I make my own tomato sauce, but I’m careful with how I use it.
Huh? How the heck are you defining a “carb percentage”? I would have thought it would be net grams of carbs per grams of serving size? Which wouldn’t change based on protein or fat content. Are you computing it as calories from net carbs vs total calories?
If so, that makes no sense to me. That would mean I could add nearly 80 grams of raw sugar to a cup of heavy cream and it would still be better than broccoli or cauliflower in terms of such a “carb percentage”.
For me, the biggest issue for tomatoes is that so many people add sugar to them when they make a sauce. However, we’re also now seeing “cauliflower” pizzas with rice flours and other starches added to the “made with cauliflower” crusts. Same for some “veggie tots” products. So any low carb veggie can have bad items added to it.
The dynamics of the comparison do change if you do them by volume (e.g. a 1-cup serving). But that would also be true of cauliflower florets vs riced cauliflower vs pureed cauliflower. And usually, when people rice their cauliflower, they drain off water, so the weight would be reduced. But the fat, carb, and protein content shouldn’t reduce much, if at all.
The percentage of carbs per 100g compared to the fat/protein. Tomatoes give you more carbs and less fat/protein than the others you compared them to.
I had to give up ALL carbs to get over the hunger and cravings. No sugar, no fruit, nothing with grains. I also gave up all artificial sweeteners (they gave me cravings). I started with easy stuff; rotisserie chicken from the deli, broccoli dipped in melted butter, cheese, bacon and eggs cooked in bacon grease. If you’re hungry, eat more fat (my go to is cheese or bacon which I cook ahead and keep in the fridge). Don’t let yourself be hungry!
Like I said, that comparison makes no sense to me. Can you point me to a web page that does such a comparison? Here’s why it doesn’t make sense to me…
A 100-gram serving of broccoli has 28 calories, of which 11 are from carbs. If I were to mix 50 grams of butter with 50 grams of raw sugar, the mix would have about 357 calories from fat and about 200 calories from the sugar, so your definition of a “carb percentage” would indicate such a butter/sugar mix is preferable to broccoli, cauliflower, or tomatoes.
That is, the percent of calories coming from carbs:
Butter/sugar mixture = 36%
Broccoli = 39%
Cauliflower = 48%
Tomatoes = 60%
OTOH, if I compare using grams of net carbs per 100 gram serving:
Tomatoes = 2.7%
Broccoli = 2.8%
Cauliflower = 3.0%
Butter/sugar mixture = 50%
Get a few bricks of cream cheese and a big bag of pepperoni or bacon. Smear, fold, enjoy. Eat until you are just about nauseated. Repeat when hungry. In the beginning eat low to no carb foods when hungry until full. You just need to wait for the miracle to happen. If you are not willing to look up nutrition facts on everything you eat and keep carbs as close to 0 as you can (lots of people aim for 20g or less) this lifestyle could make you miserable. On the flipside, if you hunker down, do your research, and don’t fudge (literally) with carbs, you might fall in love. I did.
I’m a ketchup freak, so I now make homemade sugar-free ketchup and always have it on hand.