None of this seems to make sense to me. I am a heavy rider myself (110kg). Everybody riding at the same w/kg should be moving at the same speed (outside of drafting of course). I obviously have to put out more watts than somebody who weighs 75kg but if we are both moving at 1.5 w/kg I should be able to keep up.
My guess is that the original poster isn’t using the draft correctly. If you are not drafting you will move much slower than another rider at the same w/kg that is in a good draft.
Best bet is to stay with the yellow beacon as best you can. There is usually a large group there and a good draft.
Like Peter says possibly a drafting issue. Effect of riding within group is considerable. In my first group ride (advertised at 1.6wkg) i was happily plugging away until i decided to do some shoe faffing on looking up i’d dropped off the back of the pack and had to produce 1.9 to keep up after a big burst I caught up. When i did get back within the group they were indeed producing 1.6 and I immediately only had to produce same to maintain position.
As Ricky states above, following the info in the reference, assume both riders ride at 2 w/kg. A 60 kg rider will generate 120 watts, and a 80 kg rider will generate 160 watts. On level terrain, the heavier rider will be faster. Thus, the lighter rider will need to put out 2.7 w/kg to generate the same wattage and speed.