I dunno what the patent duration is, but copyright should probably just be 50 years max IMO. If you can't make bank in that time without changing the idea up (and thus getting 50 years on the new version) you don't deserve it.
Originally I think it was closer to 20 years. Frankly I think 25 years is plenty. A quarter century is enough time to reward the creator of an IP and it respects the fact that all IP is built on top of the public domain so it's return is a natural part of the cycle.
In any case it's not like after it expires you could not trade on being the original. It's not like others could then come along and claim to have been the original creator. And if you kept making works those would each get their own period of copyright.
I agree with copyright in a sense that people should have a chance to profit from their ideas before it gets stolen, but you are right that it is way too long of a term. It stymies creativity when people can milk the same idea for many decades.
I would think for creative license like an idea for a cartoon or comic, 10-20 years is more than enough. Then they should try and make new characters or start competing with others trying to improve the character.