It's probably not correct to attribute all differences in life expectancy between India and USA to diet alone - factors like air quality are so much worse in India and play a significant role in reducing life expectancy as well. What makes more sense is to compare the life expectancy of Americans who tend to follow an Indian diet vs. those who don't. Asian Indian Americans have a life expectancy of 86-89 years [1], higher than of the US as a whole and even other asian sub groups. So the relative lack of importance attributed to protein is perhaps not as big a deal as people make it out to be.

1: https://read.dukeupress.edu/demography/article/58/5/1631/178...