If I had a 1% stake in DoorDash after the Series C, it was worth $7M ($700M * 1%). Assuming all the Series D round was new shares issued (we don't know the details), my stake in DoorDash would be diluted from 1% to 0.62% after the Series D (1% * $865M/$1.4B). However, the value of my stake would have grown from $7M to $8.68M (0.62% * $1.4B) because the valuation went up.
This obviously ignores things like value of preferred vs common stock. But, it is not straightforward to say everyone's stakes were diluted by 60% and it's bad. They were diluted, but the value of their holdings theoretically went up.
I imagine the 409a (common stock price went down), but I don't think you can infer from this that the preferred price went down. The missing figure is how many shares were issued.