Is it me or is Lavos basically the same as Galacticus (The giant Silver Surfer badguy)? Think about it..
They are both huge.
They both are, or, in the case of Lavos, have a part of them that is, Humanoid.
They both "consume" planets.
They both have something that was supposed to be beneficial to them, but this backfired majorly.
To illustrate a problem with your comparison, allow me to make a few others using the same criteria:
Is Lavos basically the same as The Dark Dweller (the villain in old cartoon show, The Pirates of Dark Water)?
Both are huge (given that the dark water is an extension of the Dark Dweller's Body, I'd say that counts as huge)
Both are humanoid (the Dark Dweller, at least, can take on Humanoid form)
Both "consume" planets (the Dark Dweller wants to cover Mer in darkwater).
They both have something that was supposed to help them but backfired (consuming Octopon, which was supposed to end the threat of anyone collecting the Thirteen Treasures of Rule).
Is Lavos basically the same as the Borg?
Both are huge (the Borg being a collective of beings far greater than a single individual instance)
Both are humanoid (we never see a non-humanoid borg)
Both "consume" planets (the Borg do so by assimilating the people on the planet and any aspects of the planet itself that they can use).
They both have something that was supposed to help them but backfired (their collective consciousness has been the downfall of the Borg on several occasions)
Is Lavos basically the same of Unicron?
Both are huge (Unicron actually being planet sized)
Both are humanoid (Unicron can transform into a humanoid thingy)
Both Consume planets (Unicron is also known as the Planet Eater)
Both have something that was supposed to help them but backfired (the creation of Galvatron, who's attempts at double-crossing Unicron helped the Autobots defeat the big bad planet)
Is Lavos basically the same as the Rockbiter from the Never Ending Story movie?
Both are huge (Rockbiter is a giant)
Both are humanoid
Both consume planets (well, rockbiter literally eats the rocks of a planet)
Both have something that was supposed to help them but backfired (Rockbiter was on a quest to help save Fantasia, but that quest ultimately leads him to his own death).
Do you see where I am going with all this? With such vague guidelines, one can compare Lavos to a lot of other fictional creatures. If Lavos was based on Galactus, judging from such criteria as you present, then it was also based on a failed 80's cartoon show, pulp science fiction, a really bad 80's movie, and a giant muppet.