Actually, at its inception, the 35 Whelen used bullets of 300 grains regularly. Elmer used 300 gr. WTC bullets (It may have even been a 350? I can't recall).
I believe Ken Howell used 275 gr. Hornadys in his Whelen for many years.
Its shortcomings in Africa is that it wasn't used in Africa. Elmer did use the 333 OKH, but had he gone prior to WWII he would have used a 35 or 400 Whelen, perhaps. When Americans went to Africa they generally didn't take 9.3's either.
Of course over recent years bullets for the 338 and 358 have gotten lighter and lighter. The 9.3 offerings really haven't changed since its inception.
Most guys using 338's are using 225 or lighter bullets today.
The Whelens shortcomings are only what we have given it; with modern, lighter bullets that's not much at hunting ranges.
Anyone worried about longer range or lack of power would be carrying a belted magnum of some sort or its equivalent.
