... is that they don't concentrate on individual stories. They're more focused on long-term stories and they subsequently take for granted the initial individual flicks.

Important to note that everyone points at Marvel as the ultimate connected universe success story... but in the first movie, the *only* illusion to an outside universe was the post-credits sequel tease, and the only illusion in the second film was, again, a post-credits scene. It wasn't until they'd proven the bankability of the individual stories that they started parsing out the info for the grander universe.

So The Mummy's biggest problem is it punted on making an interesting story here in hopes that the audience would be down for the Expanded Dark Universe greater story and what it teased.

You're right that if The Mummy would've been dope that audiences would've been all-in... but I think it would've been hard for them to make it dope with as long-term-teasey a storyline as they chose to go with here. The actual characters for this individual story are big-time duds-- it's clear where Kurtzman's attentions were.