Headphones, IEMs, and speakers all offer unique experiences. Others are right to call out the massive subjective factor that might make one more more of these options better than the others for different people. For example, one of the biggest disadvantages of headphones/IEMs is they’re inherently isolating and antisocial–it’s much more difficult to enjoy music with other people via headphones or IEMs than it is to sit in front of speakers and enjoy tunes together.
That said, I do firmly believe that generalization holds–at least as a rough guideline. I got into HiFi via speakers first, and I’ve heard 2 channel system scaling into 6 figures. Meanwhile, my headphone collection has expanded to include top-end cans like Susvara and Utopia.
As with headphones, speaker systems scale in terms of things like tuning accuracy, detail retrieval, clarity, etc. There’s a general progression where you go from audio soup to reasonably competent tuning with a few minor flaws to really clean tuning with essentially no flaws to the kind of esoteric summit stuff that sets itself apart from the unwashed masses via state of the art performance in one or more areas. Unlike headphones, 2-channel systems require unique headaches and potentially more gear as you climb up the scale–for example, room treatments, speaker placement, and the potential of partitioning out gear more than you likely would for headphones (e.g., preamps, monoblock amps, etc.).
If you’ve heard Hifiman Arya, one of its characteristic features is how smooth the delivery of audio is. It feels like it just breathes sound out–not like you’re listening to a device that’s producing audio from a recording, but like the sound is just happening. As you scale higher into speakers, there’s a similar effect where sounds become more natural, more lifelike, and the speakers themselves just disappear. That’s mostly an effect of proper stereo imaging, but the realism–the sense that if you turned around you could really believe that the performance is happening right there in the room with you–is something that you really only get out of very expensive 2-channel setups. Back of the napkin, calling that a $1700 headphone vs $17-34k speakers, that seems about fair.
Anyway, I think the main takeaway here ought to be that 2-channel audio scales way higher in price than most people realize or get to experience, and the expenses start to snowball exponentially with speakers because of all the various problems you need to solve (how to power them, how to make them work in your space without reflected sounds, etc.). There are more problems to solve, more variables, more gear, and it all costs a lot more. It’s less about headphone quality outpacing speakers than it is about the cost of speakers outpacing the cost of headphones. Both paths lead to severely diminishing returns, but speakers scale into “mortgage” numbers.