Yeah, I’m being a bit harsh. If I want stock A as a part of a balanced portfolio, and my position declines due to a price shift, it may make sense to “top-up” by buying at the lower price. Same if I am convinced that the price movement is temporary and I want to buy more to take extra advantage of a rebound (but that would apply whether I already owned the stock or not). In these cases I am doing what some would call dollar-cost-averaging. Buying in according to a systematic formula can also be considered DCA as you say. That’s not what I’m calling out.
But the idea that I can somehow reduce an historical loss on a share by buying more of it is pure “sunk-cost” fallacy. I can reduce my average loss per share (“I was down $1.00 per share, so I doubled my position and now I’m only down 50c per share, on average”), but I own more of them now. My loss remains unchanged. I’ve seen people heatedly argue the opposite.
I think we mostly agree here.