Yeah, it doesn’t really work like that.
And even if it did, gaps generated on small climbs get pulled right back in on the flat.
The only places very light people can make a difference are prolonged mid gradient (~7%) climbs, or steep climbs (over 5 mins long or you never burn out punchy heavier riders (GvA, Sagan types)).
Also, on the flat, lets say at 96kg you are doing 288W (3W/kg) using your 80W saving figure, a 60kg rider sitting in is doing 208W, but is working MUCH harder at 3.46W/kg.
In the same way that i’ll never be able to fully experience how bad climbs are for someone really heavy without putting on a 35kg backpack, I don’t think heavy folk realise how much advantage raw power gives everywhere else.