You don't have to be smart to destroy a universe with the UN. If you remember, a single stray/uncontrolled thought from Quasar would have been sufficient to do so.
Except in that particular arc, the UN had to be Fed-Ex delivered to Galactus by the F4. To me that is evidence enough that he wasn't capable of doing what you are suggesting... But w/e.
Gender: Male Location: The Fortress of Solitude in Venus
I have always though COEI AM's defeat was a complete PIS
The guy had the power of his antimatter universe which by that time IT SHOULD had been bigger than any matter universe and about the size of the whole multiverse minus 5 universes.
But COEI AM should win this one regardless if the other guy can destroy 1 universe, this is the infinite universe destroyer, he had the power of all the universes He destroyed, THUS his defeat in COEI was nothing but PIS
For instance, in that story (which we know occurred in the distant future), Tiamut had just woken up after centuries of imprisonment under the mountain... But his latest canon showings in Eternals contradict that. Etc.
^ Except this version of Galactus was incapable of summoning the UN to his location, and had to have it literally handed to him by the F4. That + the fact that Galactus has 'died' the few times he has actually used the UN, should be reason enough to assume that he wouldn't be using it here.
I agree with Galan that it could be argued as "more than CIS", when we say there is no CIS we mean fight on their capabilities and that Galactus was not as focused as others. It could be argued whether or not he can summon the UN, but certainly it has nothing to do with CIS because that by itself doesn't make you inmune to losing control or becoming an idiot.
the notion that future timelines are automatically to be treated as alternate universes is a good one, but the current Avengers - Maestro storyline and some previous Kang, Doom and even Future Imperfect seem to be extending the 'future' into the 616 present.
I mean Kang works for Maestro, thus Hulk will become Maestro () and in FF, 616 Franklin had to beg a younger Doom to save his grandfather's arse (but this led to some vague time-reset, so not quite sure).
basically, the characters, attributes and relationships are 616, just that their actions happen in a revised past or an existing future... this is quite different to the traditional "alternative universe" idea, where powers, persona, relationships are different, thus feats cannot be compared to extrapolated.
^ That would be all fine and dandy IF the Black Celestial arc wasn't contradicted by more current happenings. Aside from that, both BCA Galactus and that universe were nullified -- making it impossible for those events to transpire again.
Also there was this weird time-bubble idea going when Nebula and Kang tried to get into that reality to control Galactus. It's safe to say it got divided from normal 616 time since the time-bubble happened since you couldn't time-travel to that moment.