Stem Length

Depends how you look at it.

Long reach does not necessarily equate to a long front center, or vice versa.

Longer chainstays will equate to more front wheel grip, yes. Longer reach also tends to equate to more front wheel grip, with the caveat that it's highly dependent upon the riders body position and input through the hands.

Manufacturers attempt to compensate for the balance issues with short rears by running longer reach. The ibis hd6 is a great example of this. So is Fred's geometron g1, it has a 1.89 ratio in large with a 460mm stay, which isn't great, and necessitates a longer reach. In smaller frame sizes it is more viable though.

When it comes to descending, 1.8 is the number, there's a reason forbidden targets this, and so many people have traditionally found success sizing down on bikes, inadvertently taking advantage of the better balance offered by size medium bikes that had a "one size fits all" chainstay.