While Sentry has gained fans among Marvel Comics readership who want to see his stories continue, he doesn’t quite fit into the publisher’s plans. As a hero, he’s so powerful that his abilities can overcome nearly every threat thrown their way. The only way they’re challenged is through him losing control and the Void emerging, a storyline that’s been done over and over. Sentry’s return would create a similar problem to introducing him in the MCU — nothing can ever top him, unless you nerf his powers, which defeats the whole purpose of having a hero with the capabilities of a hundred million exploding suns.
The MCU can circumvent these storytelling issues by using him as an all-powerful one-off character, but the comics have repeated his arc so many times that, on the page, it now feels monotonous.
Ultimately, Marvel Comics created this problem by continuing his story past his original miniseries. The hero being forgotten a second time, becoming Marvel’s most important hero nobody remembers, would have served as a fitting end for Sentry. He was written to be a one-off character, not a continuing one.
Instead, he was reintroduced, joined and fought the Avengers, lost control, and was killed multiple times with no apparent direction for the character. Sadly, unless something radically is done to his story, like him becoming the Revenant-Prime in “Strange,” there really isn’t a place for Sentry right now — or maybe ever. He’s an incredibly cool hero with a terrific premise, but he can’t fit as a continual presence in the Marvel Universe without really messing up the power dynamics. And when he enters the MCU, they have to learn these lessons and apply them carefully.