Earlier quoted context omitted.
There are plenty of very healthy meat-avoiding people in the world. Malnutrition is also a problem in the world. Malnutrition from people eating fake meat? So far, not a problem.
The question is how feasible it is? Is it a trivial change in lifestyle? Is it more expensive or cheaper? Can you make it work with the basic fare that you find everywhere, or do you need to shop around for plant products that are more exotic?
In my experience (omnivore -> vegetarian -> vegan), going vegetarian is not too difficult. Going something like pescatarian, or even just eliminating red meat -- that's downright easy. I am not a particularly great cook, but my grocery bill dropped noticeably when I went vegetarian because I was buying more vegetables for the first time in my life. Even when eating out I had to make very few adjustments. Most restaurants around me have great vegetarian menus. I feel like it's not a particularly difficult transition to make.
On the other hand, going vegan was harder. Part of this is how good you are at cooking. Part of it is that you have to research a bit more. I take supplements (D3, K2, B12) as a vegan. I never worried for a second about my nutritional input when I went vegetarian. And again, if you're going pescetarian and still eating a fair bit of cheese/eggs, I just really doubt nutrition is a concern for most people. But after going vegan, suddenly I had to actually think about some of these nutritional questions that I was able to ignore before because I just ate a lot of eggs and cheese.
You can make veganism a lot cheaper (and plenty of people do), but I'm lazy and bad at cooking, so I buy more specialty vegan products, which are expensive. I put up with it, it's fine, it's doable, but being vegan is annoying sometimes, and it requires more work.
Again, it's doable. It's fine, lots of people make it work, I make it work. You can be vegan and healthy. But in terms of effort/work to be healthy and to keep costs down, I think that veganism and vegetarianism are in separate categories.
But importantly, you don't need to go vegan to see improvements here. If you're talking about "meat-avoiding" in general, just getting rid of red meat from your diet will have a positive environmental impact, and will probably be both healthier and cheaper as long as you put at least a tiny bit of effort into not just eating only Impossible burgers and mac&cheese. You can already in many places get raw tofu significantly cheaper than red meat, and after that it's really just learning how to make stir fries and figuring out 'new' foods like mushrooms and beans.
Part of the benefits here are that in general, most people who aren't following a specific diet probably shouldn't eat as much meat as they do anyway. So if the end result is that you eat one serving of plant-based meat alongside some eggs/veggies/beans, instead of three servings of steak, that's very likely to be both healthier and cheaper.