Re Gay: He already had plenty of speed background to run 19.58 from previous years, so this was not a development, but, rather, a stimulus to the execution most likely chosen because of a serious quad injury that kept him at Dr Wolfhart’s clinic in Germany for two months last winter.
Point 1: As in weights to an extent, this can be true but not in isolation and sufficient speed must be in pace to run high enough quality SE.
Higher speed capacity will allow for higher SE results but higher SE results may not necessarily lead to higher speeds over 100m- the key to higher performance in top 100s now that improvements in endurance capacity over the final 20m have been used up and higher speeds are the key (.81 segments now!)
Including a standing start, a 31 sec 300m is terrific be still averages 10mps, and does not guarantee ever reaching above 12mps.
Point2: Possible but does it need to be continuous to be effective? Ben was doing 24 x 60 in early 1985 (similar to Mennea). By your math, 2 x 300 = 26 x the upright volume of one 60 at a lower speed, while 24 x 60 = 24 x the vol at a higher rate, yielding more extension etc.
Point 3: This is certainly possible and is likely the most tolerable route for a majority of developing athletes.