Stems.
To me, they are nearly everything. Not everything, but nearly.
The debate between older briar and newer briar is a valid one-old briar such as from Barling's (pre transition, way way back) has ancient Algerian briar aged in some cases near 100 years, and for those folks who feel that ancient briar is the only way to go, excellent.
On the other hand, frequently, engineering can take a back seat for those involved making ancient briar. I have several Barlings and Dunhills that are quite old, but the stem work leaves everything to be desired. I own a 1925 Bewlay with an orithic stem (round type stem frequently used in the past) that smokes very well, but the stem, well, just sucks.
To sum it up, stems (with appropriate engineering which we are not discussing here) are nearly everything. Just smoke a pipe made by Rad Davis after 2006 and that will answer any doubts about whether a stem matters or not. Jerry Crawford, Scott Thile, Michael Parks, Clark Leyton, just to mention a few. There are so many modern craftsmen who have studied stem work and their degree of importance.
These gentlemen (who mostly make vulcanite stems) know how to cut a stem. (apologies to the very many that I left out)