Thinking about mid-caps (DON) in particular, and what they might offer me

SCHD holds a significant percentage of my portfolio. I’m a retiree and I like the fact that SCHD is steady and boring. I like steady and boring a lot. I’ve been thinking about opening a position of DON, also nicely steady and boring, to add some diversification through mid-caps, but the finances are throwing me off. I look at SCHD with a much lower expense ratio and a higher yield, and I see DON, between expense ratio and yield, with a significant drag. That drag is money I won’t get that I could either spend down or reinvest. As a mid-cap, DON also carries a slight risk in terms of volatility which makes me think that should I have to sell for any reason, with a more volatile mid-cap, the odds are higher than I could be selling at a lower value than I’d like. Probably low odds with that possibility, but still a small factor. Finally, DON is a little less tax efficient than SCHD.

So I’m trying to figure out what DON brings to my portfolio that I’m not seeing. Reasons why I might want to take that drag and sacrifice some passive income and why that mid-cap type of diversification is necessary or important for a retiree. What does a 7%-10% holding in DON do for me?

TL, DR: I’m thinking if I should be DONE with thoughts of DON?