No 'BUT' about it, 8 under par is 8 under par,62 around Birkdale in Open Championship guise is amazing,Jonny Millers 63 around Oakmont was also 8 under the par of 71.
When I played at Birkdale,as a single figure handicapper,off the front tees,with members pin positions and wide fairways I could not break 90 playing well,8 pars 4's well over 450yds 3 of them very close to 500 yds it's a par 70 technically but at c7200 yards it's a monster.As for St Andrews,I've played the Old Course once,you really can hit it all over the place there,massively wide fairways and huge shared greens,it's the Home of golf and deserves its place on the Open rota but there are far more challenging courses,especially for the pros.