Express was added to Hagrid's in May last year. The timeline doesn’t support Express being the root cause. The highest spike occurs when JPRA goes down, which removes a major people-eater from IOA. On top of that, we can't just outright ignore that we’re in a Northeast school break window right off the heels of a big holiday weekend.
Removing Express might make standby move a bit faster per hour, but it doesn’t change Hagrid’s capacity/demand. It's still a big reason people wake up at the crack of dawn for IOA's EPA (along with VelociCoaster). You’d likely still see long waits, just without the premium options that support hotels that
@Clive mentioned.
From a business standpoint, since Express is baked into Premier hotels and Premier APs, taking the park’s most popular ride away from would devalue some of Universal’s highest-tier products overnight. That’s a pretty drastic move for something that probably wouldn’t meaningfully reduce waits in the long term.