Are IEMs are Really better than headphones?

I have been digesting what I believe is an important review from DMS on the Mega 5 EST, published on YouTube 11 months ago.

https://youtube.com/watch?v=vWWofORMPZU&si=tKqIUEOOXTa89dPc

Before I begin, I do like DMS’ videos, but I am not particularly a fanboy of DMS more than any other audio reviewer. I try to consume a variety of audio review content from different sources and I have watched Super Reviews, Crinacle, GoldenSound, Resolve, DMS, GadgetryTech, Josh Valour, Timmy V, Jaytiss, Jays Audio, Listener, Caleb Loo, Zeos, Passion for Sound, and many other reviewers. This is an attempt to gather information from a wide variety of sources. I also read online discussion forums, reviews, and go on discord on several channels.

Why would I put any stock into what DMS says if I have my own 2 ears? I can’t test as many products as an actual audio reviewer. It would be akin to the fact that I’ve seen paintings before, but I would trust an art history major to be able to more accurately identify what’s happening and provide historical context and insights on paintings.

With that said, during DMS’ review of the Mega 5 EST, he states that he likes the IEM better than any of his headphones. He’s making this statement agnostic of the price of the headphones. I don’t think people really felt the impact of the statement and the video only has 75K views whereas other videos like the headphones.com 2023 tier list has over 300K views. He also says he grabs the IEMs to experience the most “detail” in his music, and by extension he is saying that IEMs are giving him a better detail experience than headphones. Any headphone. He does mention HE-1 as a potential competitor for details but they are so far apart in price it’s almost unnecessary to discuss.

With many IEMs that are coming out with similar tuning as the Mega 5 EST, I don’t know if the main focus point of the video should actually be the Mega 5 EST or whether the main focus point should actually be the preference that a major headphone reviewer expressed for IEMs over headphones, at least in the area of FR and detail retrieval.

What do you all think? Have I misinterpreted DMS’ message? Is there something you think you can only get in a headphone but not an IEM? Was DMS missing something critical like soundstage in his analysis? Is there a headphone you feel is more detailed than any IEM (contrary to DMS’ assessment)?