What would you say is THE MOST important factor to good imaging?

Utter nonsense. If you can’t get horns to image, you are doing something wrong. And horns are a lot more directional than planars.
You are very confused.

Amen to that Ozzy.

THE MOST important factor to good imaging?

The Preamp

There is only one , get everything right  . You can get a decent system  from the buy and try necessity for about 100 K .

@douglas_schroeder ....the Legacys' have all the means to accomplish 'what they do' with the room correction, the amt tweeters, and it's other details.....

I've accomplished basically the same for +/- 2% of their price.

The rest of the $ I'll apply to my speakers...;)

As is said: "Priceless."

...and I agree with Wolfie62....if it's not in the mastering, you can't fix it.

'Pig's ear>Silk Purse' still doesn't exist....

Yours Conceptually, J

The weakest link.
You can’t answer this absolutely without context. There are multiple conditions that are necessary without being individually sufficient. You have a series of elements aimed at producing a desired outcome. If any of them are inadequate the outcome will suffer. A perfect hardware chain from power to room acoustics would be useless with a mono recording.