Is the preamp the “heart” of the system?

noooo way....really?

being educated by this portal...I'd say...its power cords!

The preamp May add colorations, be less pure, add distortion, etc, etc...  I don’t particularly care.  My desire is to have an engaging and enjoyable system that delivers an extraordinary listening experience.   The “purer” the sound tends to be the less engaging on many recordings.  

You are correct compared to going amp direct, or using a "good passive pre impedance matched, an active preamp will add coloration's, distortions and also have less dynamics. 
If you need this from an active preamp give this to your sound, then I say do something about your source to fix the problem, and then flick that expensive active preamp altogether.
The old saying continues to be correct "the best preamp sounds like a piece of wire", guess what that's what going direct sounds is. 

Cheers George

coming from a cath lab background, the pre is the Brian’s of your system and the amp the heart or power.  Pre makes decisions and the amp will follow. But in the end, who cares what normanclature you use to describe your system, just enjoy and follow what your looking for in the end.

Pre makes decisions and the amp will follow

Ho dear!  and if the pre is not totally transparent and free of distortion as the best pre in the world is "suppose" to sound "like a piece of wire" it's said. Then it's coloring and distorting the sound of the source.
For it to sound like a "piece of wire" it would then sound like the source direct to the amp.

Cheers George 

YES