I'm not so sure about that theory.
2005 Ford Focus ZXW base kerb weight 2775LB
1985 300TDT 3571LB
1992 Volvo 240 wagon 3133LB
VW Squareback 2227LB
If I had to choose a head on collision between the focus and the squareback, I would put my money on the focus. W123 vs Focus might be more interesting.
https://www.youtube.com/watch?v=SeMrOQfliCs
https://www.youtube.com/watch?v=4oPVESVlhPU