Back to the orignal point - Kyle Godwin has not been an 87kg player for a long time.
That is, unless his thighs are filled with air.
He has had no issue defending at 12 in Super Rugby yet. If anything, his defensive work was his best attribute this past year.
Kurtley Beale is listed at 90kgs. Weight means absolutely shit when the measurements are outdated and some players are literal leagues ahead of others when it comes to taking contact.
Horan and To'omua have almost identical measurements so your whole "other era" argument is complete garbage too.
Actually, where did you even pluck that 87kg number from? His U-20s profile? The Force AND Wikipedia have him at 93kg. Just stop.