England: Ben Earl - 1.86m / 110kg (BMI: 31.80)
France: Gregory Aldritt - 1.91m / 115kg (BMI: 31.52)
Ireland: Jack Conan - 1.93m / 110kg (BMI: 29.53)
Italy: Braam Steyn - 1.94m / 110kg (BMI: 29.23)
Scotland: Magnus Bradbury - 1.93m / 115kg (BMI: 30.87))
Wales: Taulupe Faletau - 1.87m / 110kg
Always interesting - I did something similar about 2 years ago, when again, people were saying that Mercer was too small, so we should pick Simmonds instead (at the time, Zach was 105kg, and I was saying that I expected hos playing weight to stabilse around 110-112 - his currently quoted weight is 110):
Zach Mercer: 190cm; 110 kg (BMI: 30.47)
Sam Simmonds: 184cm; 102kg (BMI: 30.13)
Ben Earle: 186cm; 110kg (BMI: 31.80)
Lewis Ludlam: 190cm; 110kg (BMI: 30.47)
Mark Wilson: 191cm; 112kg (BMI: 30.70)
Louis Picamoles: 192cm; 116kg (BMI: 31.47)
Sergio Parisse: 196cm; 112kg (BMI: 29.15)
Taupe Faletau: 187cm; 110kg (BMI: 31.45)
Jamie Heaslip: 192cm; 110kg (BMI: 29.84)
Kieran Read: 193cm; 110kg (BMI: 29.53)
David Pocock: 183cm; 103kg (BMI: 30.76)
Billy Vunipola: 188cm; 130kg (BMI: 36.78)
Nathan Hughes: 196cm; 125kg (BMI: 32.54)
Ben Morgan: 191cm; 116kg (BMI: 31.8)
Thomas Waldron: 185cm; 114kg (BMI: 33.31)
The only reason people seem to think that 110kg is too light for a #8 is Billy Vunipola; who is an absolute physical freak. There is no-one in world rugby even close to him in terms of physical stats without playing front row.
What you're used to skews your perception of "normal" - I have big dogs; normal sized dogs look tiny; I have small cats; normal sized cats look huge. England have a huge #8; all other international #8s look too small in comparison. However, looking at the list of top international #8s, someone like Mercer really isn't giving up much already.