"But a pilot still has to be able to balance the tandem and stoker, so it is important that he'd be able to get both feet FLAT on the ground."
1. If the team starts off and stops on one captain foot and one stoker foot, the captain DOES NOT have to balance the tandem and the stoker.
2. If it is possible to reliably board and start off and stop on one captain foot or one stoker foot, then it is not important that the captain be able to "get both feet FLAT on the ground."
A quick check of Litespeed's thread, "stocker in or out", easily found near the bottom of the first page of threads, finds two posters (ncernitz and mlwschultz) who are part of teams who start off and stop on one captain foot and one stoker foot. No doubt there are many others. Are they all wrong? Is what they say they are doing impossible? Are the stokers more or less likely to get "dumped" with one foot or no feet on the ground? There is probably also a significant percentage of teams that start off one foot.
I would like to see people coming to this forum for advice on a significant purchase objectively presented with the full range of choices. That includes methods and materials.