Tried swapping butter for coconut oil in pound cake - total disaster

Honestly, the same thing happened to me with a lemon pound cake last spring. I did a 1:1 swap like you and ended up with this greasy, dense brick that barely rose. It was so disappointing because I thought coconut oil would be a healthier swap, but nope. Tbh, that person in the video you mentioned is totally right about the water and milk solids thing, butter really does the heavy lifting for structure. I tried it again later with half coconut oil and half butter, and even then the texture was just off, not as tender. Ngl, I've just given up and stick to butter for anything that needs to be fluffy now.