stacking passives on champions

Ok, so i opened this thread because i think all the champions with stacking passives such as Nasus, Sion, Thresh, and Veigar are unneeded. To put it simply i think the stacking makes them to strong in the late game as i myself have seen and have done 5v1s with all and taken 3 to all of them down. Now i dont think this should be possible the only reason I was able to do it was the simple fact that i had a stupid amount of stacks and i built defensively and let the stacks do the work and yes this is included on veigar i don't need to stack pure ap on him. i simply build hp ap items stack my q kills and grab 1 defensive items in magic resist and 1 in armor . I don't think its even right how high they can stack now i understand that there is a soft cap but even still i have 1 shot people with Nasus and Veigar while Thresh and Sion dont seem as strong with the stacks . This would be mainly based on Nasus and veigars late game just being down right bull****. When fighting it i find it far to strong and when playing it i feel like a god and get almost bored with how easy it is to just annihilate. Anyways this is my thought please share yours why there to strong or why there not maybe i will learn a weak point i myself didn't see.