I think the importance of protein is over-estimated, and people go a bit nuts on trying to get loads of it when they probably don't need to. Protein seems to be the new nutritional fad in marketing; it's always been a thing for bodybuilding, but there's a wave of new mainstream products which market themselves as having loads of protein - there's an ad campaign in particular that's all about people pulling all-nighter saying 'you need protein'.
I recently calculated my average daily nutrition as I'm trying to get enough to gain weight, and I discovered that even without protein shakes I was getting plenty of protein but not enough carbs. I think this is probably where a lot of people go wrong as they focus on protein and forget about the carbs, which you also need to gain weight.
On the whole though, fitness and nutrition is a minefield of misinformation. I've been told so many different things from so many people who all think of themselves as self-taught experts, yet I doubt any of them could say how exactly they know all the stuff they spout. It's a weirdly personal issue, and people seem to have strong feelings about what they think is correct. You just have to learn to tune out what people try and tell you.
The importance of protein isn't over estimated, especially if you train, then you need the amino acids for muscle recovery but that is a different issue when talking about weight loss or weight control because we are talking about building muscle rather than losing weight.
Fitness and nutrition is a minefield of misinformation because the only thing most people read are fitness magazines or the daily sensationalist story telling you that eating broccoli every day will put ten years on your life or some other similar shit. You're right though, there is nothing like diet and weight loss to polarise opinion because most people have a lifetime of misinformation to correct. I have read deeply on the subject over a number of years and know more about diet and cholesterol than most doctors, who surprisingly know very little. Most even find that hard to believe. The government and the medical profession got it wrong for years in blaming fat for heart disease and obesity, Ancel Keys has a lot to answer for.
Most high protein shakes and bars etc still contain a lot of carbs, even refined sugar, so any benefit you might have had from not spiking your blood sugar is lost. If you want to read the definitive text the read 'Good Calories Bad Calories by Gary Taubes' it is the best book on diet ever written and it is meticulously researched with a long and detailed bibliography. The conclusions are not his, they are naturally drawn from all available scientific evidence.
If you want to gain weight then yes you should probably eat more carbs, especially simple carbs but be prepared for the potential that some people simply do not have the same amount of lipophilic (fat) cells, or the ability to put on weight. That is the genetic factor and it's why we don't get fat on the back of our hands... There are no lipophilic cells there, equally, some of us (not me) have a low incidence of lipophilic cells in other parts of the body and therefore will always struggle to put on weight. It's very easy to discount genetic factors but weight loss or weight gain is rather more complex than diet.