In terms of stat collection - already done for you:
https://www.therugbyforum.com/threa...-england-04-02-2018.40642/page-16#post-887406
Zach Mercer: 190cm; 105 kg (BMI: 29.09)
Sam Simmonds: 184cm; 103kg (BMI: 30.42)
Louis Picamoles: 192cm; 116kg (BMI: 31.47)
Sergio Parisse: 196cm; 112kg (BMI: 29.15)
Taupe Faletau: 189cm; 110kg (BMI: 30.79)
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.
I know, I know, people say that there's absolutely no way Mercer can be 105 kg - because of their perception bias (or they're thinking of him a year ago). Stand him next to Billy; and he's lightweight. Stand him next to Faletau; and he's a little smaller; but there's really not much in it; mostly upper legs- lower torso.
ETA: Different stat.s available for Zach.
RFU = 103kg
ESPN = 104kg
Bath = 105kg
Wiki = 105kg
RugbyProfiles = 108kg
For those interested; Charlie Morgan one of his usual excellent write-ups of Zach a couple of weeks ago:
http://subscriber.telegraph.co.uk/r...s-want-see-zach-mercer-back-premiership-duty/