Absolutely not - I am very adverse to feeding natives unless they are poor do-ers. A broad spec balancer is acceptable with a handful of chaff, but I would certainly not be even contemplating more than that.
I feed my 12.2 NF (2yo) the top spec antilam feed balancer, some happy hoof (lami trust) and some speedy beet (lami trust). He is out in a field 24/7. Looks great on it, not fat and the feed he is fed has lower calories/less sugar than the grass and offers the correct balance of vits and mins etc.
I personally feed all mine, always have and always will no matter what the breed. My natives get some chaff along with an all round vit & min supplement (as well as they're usual other joint supplement etc.).
I really only feed so they can get their supplements. But I think ANY horse needs an all round vit & min supplement, IMO especially natives since they are usually on restricted grazing so are missing out on nutrients.
Ditto Weezy. My native ponies are on nothing but restricted grass (starvation paddock) and hay. Except the 2 mares are being fed at the mo due to being in-foal. People always forget where NFs come from- the forest where there is no lush grass or hard feed, they really do live on fresh air.