I mean, I absolutely think Galactus should be connected to the Celestials. They've established a race of giant armor-wearing cosmic godbeings, it would be silly to have another giant armor-wearing cosmic godbeing who is completely unrelated to them.
That said, I lean in the direction of Galactus as "Celestial Predator". His purpose in existence is essentially to eat Celestials. Does this make him a villain? Well, not intrinsically, because frankly the Celestials don't really merit that kind of moral high ground. However, it does make him equally dangerous to life lower on the cosmic hierarchy, since whether you die because the Celestial embryo in your planet hatched and cracked it open, or because Galactus cracked your planet open to eat it first, you are still dead due to cosmic forces beyond comprehension.
( So, why would Galactus come for Earth? Because while Tiamat is "dead", death for a Celestial is a relative thing, and hasn't changed its 'edibility'. Thus, Earth is basically the ultimate meal for Galactus, a planet whose Celestial embryo is 100% mature, but still sitting their helpless waiting to be consumed. Normally he doesn't get to eat Celestials that mature, since before he reaches the place the planet has already popped and the Celestial is free to fight or escape. )