Well, since I'm the frontman for T5SS, and it presents the harsh retcon, I'll put my two Credits for why...
The Marches are the starting core for any potential newbie referees, and forcing odd explanations on them to the google generation is just cruel.
So, in the Marches (at least), I make a strong argument for simple explanations and forcing everything to conform to some harsher realities than Supplement 3 was matched to.
Rob follows the beat of a different drummer... but in 1981 I was barely in high school, and the father of one of my players was what I guess today would be an astrophysicist, and the other was assistant to chemist who got thanked by two Noble prize winners. My father was a Pentecostal minister.
Making me as a high schooler explain the Spinward Marches was a cruel thing I would not inflict on anyone else.
And I like the Shriekers, so I support the simplest path, which is the ugly retcon. Or, as I asked Marc on this: there's three canon facts, only two of which can be true. You pick the two, and we'll explain those.