I think it's an odd thing to say really - unless the horse really is puny & a real wimp & just wouldn't stand up to the required fitness level. Could said wimpy horse not then do a bit of SJ or do dressage..?
Some people have preference to heavier boned horses but then let look at the Anglo Arab who won Badminton a few years back, he was very light indeed. One of the YR individual horses last year has barely 8.5 inches of bone and she's 2* so I'm not sure I'd ever say any horse is 'too light' to do anything. Its just personal preference.
horses r bred to do different things though - theyre bred to be light but with bone to do eventing, heavyweight for farm work, lightweight for racing etc it just depends on personal reference (as sevenmiles said lol!) ;-)
I am shocked that anyone could think that, there is no such thing as 'being too light to event'
A lot of the Rock King horses are TINY- if you ever see Rock Model, King of the Castle/Rock Chick,Penny Lane,(all international/ good eventers) they ALL have TINY bone- I would say less bone then my two flat race bred TB's. Rock Model prob has under 8 inches of bone and King of the Castle even less than that.
thats very true about the RK horses (or most of them!) one of mine has less than 8inch for sure, shes a real toughy and finds advanced easy! the exception is the other RK who is built like a big warmblood! King of the castle is very light isn't he.
PF isn't exactly on the chunky side and yet she's tough as old boots. I suppose though part of getting her that way is that (aside from when she was in training, presumably) her workload has been increased very gradually and I watch her legs like a hawk.
Ps; I know PF doesn't event, but I'm sure she could if I wasn't such a coward