I don't really see the connection between "battling nigh insurmountable odds" and "it's just corny," tbh. Like, those two things don't seem to be related to each other.
I'd also point out that Cortana's not omniscient or omnipresent; she's wherever a connected human or forerunner terminal is, true, and she's very very very smart, but that's not the same as either of those. In a way, it's sort of an extrapolation of what it's got to be like to fight a modern developed nation as a resistance force. Their resources and knowledge gathering capacity vastly outstrips your own. If they can pin you down, that's that.
I can see the appeal there.
when it comes to her principal enemy, she is essentially omnipresent and omnicient.
Omniscient: She has just about all of their AI, and with it their entire knowledge base: there locations, their logistics, their tactics. Remember when the Covenant would have been happy to get their hands on just one AI? Now the bad guy has all of them. It's corny.
Omnipresent: Again, if she can be at any terminal, for all intents and purposes she her goonies can be anywhere our hero's are at a moments notice. No doubt, they'll have to come up with some currently unknown limits to her power so that they can build a game around it, but it's likely to be forced given what we know AI like Cortana are SHOULD BE capable of according established lore when it comes to multitasking and multi-locating. We see her (and BB) do some CRAZY shit before she had access to the domain. Now there's that crazy shit on steroids to contend with ...
Seemingly insurmountable odds are not inherently corny. But what makes such stories interesting is when the antagonists weaknesses and the protagonists strengths are well established and believable. That's what we had with the UNSC, the Covenant and the Flood. And I haven't seen any of that foundation being built in H4 or 5. The "plucked out of thin air" nature of this conflict and its odds is what is corny to me. Can't wait for another Dues Ex Machina to even the odds like in H4 /s
Really doesn't feel like a good "resistance force" story is brewing. I love a good, " they got the guns, but we know the terrain" story. But it appears they got the guns AND know the terrain, if the established lore is anything to go by. I'd love for them to create a compelling story and honor everything that's come before, but I just don't see it.