1) I wouldn't 100% agree with this. It's not that speakers sound "better" than headphones, it's that speakers don't require any tuning to match a person's specific physiology (e.g. shape of their ears, ear canal) but the other things do. When you use headphones, you still use your whole ear canal but the sound is distorted by how the headphones interact with your ears, particularly the pinna. When you use IEMs, you only use part of your ear canal and skip the pinna entirely, so the sound can't sound as natural as speakers do unless you compensate to reintroduce the effect of the pinna/canal. This is all possible to varying degrees. EQ helps a lot and there are ways to measure HRTF as well.

2) Absolutely and it's constantly getting better.