Have Emerging Markets ever outperformed?

I've tried Googling this question and read several articles, but I can't seem to find anything indicating the historical performance of Emerging Markets.

I currently own global equities, market cap weighted via ETF's. I've played around with the Portfolio Backtest Visualizer, and it seems in all instances where Emerging Markets is included in the portfolio, it underperforms an equivalent portfolio that excludes Emerging Markets.

So it got me thinking, does it really make sense to have Emerging Markets exposure? Or are we just creating a drag on portfolio returns in the name of “diversification”?

To me, I think owning US & Developed Markets (Canada, Japan, EU, Australia, South Korea etc.) is more than enough diversification, and having Emerging Markets is just “diworsification”.

Any thoughts on this?