Are they comparable? Yes, they both have strengths and weaknesses when compared to each other. Over-ears (especially open backs) generally have better and more natural soundstage, but the iem more in-your-head type sound feels (to me) like more details is crammed into my ears. The rest of it is down to the specific iem and headphones imo. For example, I have the sundara and b2d, they’re both in the same price point. Sundara’s bass isn’t particularly special, but it still feels more natural and just plain better than the b2d to my ears. That’s not because iem bass are inherently bad, it’s just that b2d specifically doesn’t have a great bass. If I heard another iem that’s known for their bass I might think that sundara’s bass is bad this time around.

It’s really down to use case tbh, I can’t bring my full sized headphones out on the street, can I? (Technically I can, but you know what I mean). And I certainly don’t want to sweat in my full sized headphones when the weather is hot. That’s where iem comes into place: when I can’t, or just don’t want to strap a full sized can onto my head.