The problem with late game reliant champions

People say that the late game of champs such as Poppy, Veigar and Nasus is balanced due to the lack of early game power that these champions have. To this I call bullshit, the powerspikes of a champion shouldn´t be considered when balancing a champion. Sure, you can probably try to smash these champions early game with a few champions (ehem riven) and most other picks will need help of their junglers, but that´s the only counterplay that you have against these late game champions and even that can be countered with the help of their respective junglers. A champion´s bad early game shouldn´t be an excuse for the stupidity of their late game. A balanced champion should be one that you can beat at any stage of the game by exploiting its current weaknessess, a late game champion has little to none weaknessessn that you can exploit during a skirmish. And its not like you will always be able to end a game in the early mid stages of the match, most games go on untill the 35-45 min mark when these late game champions only need the 25 min mark to stablish an unstoppabble threat at which point weaknessess dont matter and it is just a thing of having a 5v1 to kill that one champion while probably loosing 1 or 2 guys. A game will only end at the 20 min mark when the match is just unbalanced, where the 5 summoners of one team will just be superior to their adversaries and go in 40-10 game, but lets face it, those games are no fun. Champions should have an exploitable big weakness if they have a strong device at their mercy AT ALL POINTS OF THE GAME, stablishing a weak early game as that exploitable weakness is just for me poor design in the champion and a lazy excuse to not make the champion better.