As others have said, it’s unclear as of yet what state the Infinity will be in during the events of Infinite (it seems clear that it will be hobbled at best, and that it could be destroyed entirely, but there’s no hard confirmation one way or another). All this is to say that it very well may not be down and out forever, we’ll just have to wait and see. It could be lost with all hands, or simply grounded and temporarily out of commission like we saw in Halo 4.
As for what it could/should have been in the stories to date, I agree that its potential wasn’t ever really fulfilled in Halo 4 or 5. SpOps is really the best implementation of Infinity we’ve seen in anything yet, and even SpOps failed to quite sell me on its status as a juggernaut behemoth.
While it dwarfs the ships that comprised the H/C Era human armada, the Infinity doesn’t ever seem particularly invincible; in the H4 campaign, we only ever see it helpless against the Didact-- in SpOps, there are numerous occasions when it’s infiltrated and substantively threatened by Covenant and Promethian boarding parties, and in Halo 5, it only narrowly escapes the grasp of Cortana and her Created.
Of course it wouldn’t be interesting or narratively valuable if the Infinity represented an insurmountable threat to any of the UNSC’s enemies, but it should at least represent a very solid bulwark against Storm Covenant and Promethian aggression, and it never seemed to intimidate either of those factions to a degree that justified its in-lore reputation. Certainly, from what we’ve seen of Infinite, it didn’t do anything much to dissuade the Banished from launching a devastating assault on UNSC forces at Zeta Halo.
The Infinity is certainly impressive on paper, but the “show, don’t tell,” element of demonstrating its power and utility as a real game-changer for humanity in the storytelling hasn’t really been accomplished. I’m hoping that Infinite gives it a more meaningful role, either as the endgame objective (Chief’s ultimate goal being to get it back in action to turn the tide against the Banished) or as a powerful “last-stand,” that accomplishes something truly valuable for the UNSC’s efforts against the Banished.
Whether or not the Infinity makes it through Infinite, I do hope Lasky and Palmer survive (Roland, too!). Although I think these characters haven’t been utilized phenomenally to date, seeing them cope with the total loss of the Infinity (or even a situation where it just seems completely hopeless) would be a great place to flesh out and develop their characters through palpable adversity. And, honestly, it would just suck to see Lasky die- he’s honestly one of the most likable and sympathetic characters in the history of the series (this is a good and a bad thing), and seeing him die without getting a chance to get at least a glimpse into a darker side of his character would be a shame.