Is Sound Stage an artifact of recording?

It’s largely  a matter of perspective at an acoustic live event.  Where are you located relative to the players?  Usually not very close and you hear as much or more reflected sound than direct. 
 

Recordings are similar but different.  The producers and engineers control what you hear as part of the production process.  Similar scenario when electronic amplification, mixing and production is involved with a live concert.  
 

Every recording is different.  That’s part of what makes them so interesting. 
 

A concert hall has a huge advantage.It was expressly designed to have excellent acoustics. Rooms at home are not.

I regularly go to operas and concerts. At times I can pinpoint instruments, especially percussion, but mostly not. 

Creating a "sound stage" on recordings is an attempt to recreate that sound environment at home. It is a nearly impossible task. The best approach to recording orchestral music is to place microphones in such a manner that the "concert hall" experience, not a "sound stage" is reproduced as accurately as possible.

Classical music and operas are unique in this respect. Other types of music rely on electronic effects (both during and post recording) to achieve desired results. Recordings of live performances usually have more energy than studio recordings but suffer from the mistakes that are usual in live performances.

I think you're referring more to "imaging" than a soundstage.

Yes, at a live event the images are definitely more diffuse than what I hear on my system.