Well, we were discussing equities, no?
Bonds: While an individual EM company may be more solid in contrast to its equally rated US company, the whole point is that the EM company has a systemic tail risk which is greater than the US company.
Even the most solid company can quickly tank when its geographical surroundings collapse. Ukraine, Greece, Venezuale, Argentina: casualties aplenty. In a non-crisis year this means indeed on average these companies should perform better. Until they don't and implode. It's how the rating system works.
If you are arguing rating agencies are imperfect, no-one is going to disagree with you here I believe. To what extent markets haven't recognized tail risks in the actual yields (both bonds and equities) and may underestimate or overestimate certain risks, that's yet another discussion.
On the whole, I believe indeed EM, both equities and bonds, are structurally somewhat cheaper than they should be. The added volatility though is a big trade-off. It's why I went in EM a bit but not all-in myself (+10%) last year, although I'm reconsidering this with the recent run-up.
All in all, buying Unilever is I think likely as good as a trade-off between safety & returns as the somewhat EM company Carver (Korea) that just got bought by them. Of course, if I really knew the answers ...