Hello, I recently bought these and I'm having exactly the same problems: the noise reduction is almost non-existent. I also have to push them very far into my ears to get a slight impression of noise reduction. If I deactivate it, I hear almost no difference. For voice assist, I had to go into the settings in the Sony app, System tab, Volca Assist, and choose "Mobile device voice assist function". Then, when I press and hold the right earpiece, Siri is activated.

1. I have both XM4 and XM5. I have found XM4 easier to fit. Some people have the same complain as you do and recommend using
earpieces of other manufacturers. Do Google search.
2. Yes. XM4 has the voice assistance feature but XM5 does not.

I was also disappointed with the ANC function, especially compared to the Sony closed headphones. On a plane, the ANC of the WF-1000XM5 is probably ineffective compared to the really pleasant ANC of the closed models.
I find the seating comfort pleasant, even over longer periods of time. The sound is very balanced and pleasing.
Unfortunately, the complex functions can only be controlled via the smartphone app, making them unusable for me as a PC user.
The beeps annoy me less than the voice in my head in flawless Asia English "Noise Cancelling Off" - not a minus point for me.