Doctor Strange in the Multiverse of Madness' Illuminati sequence features cameos and references to the Marvel Comics and Marvel movies outside the Marvel Cinematic Universe. However, the most surprising was Reed Richards, played by John Krasinski. His appearance is unique, as while the other characters that make up the Illuminati are references to other forms of official media, Krasinski's Mister Fantastic seems to be a tongue-in-cheek nod to a popular piece of fan-casting.
That was a deliberate move on the part of the creators, with Sam Raimi stating that Kevin Feige told him it was up to them to "make that dream come true." However, given Mister Fantastic's small role in Multiverse of Madness, Krasinski doesn't seem the best fit for what appears to be a one-time cameo. A much better choice would have been letting Ioan Gruffudd reprise his role from the 2005 Fantastic Four film.
That's not to say John Krasinski was a poor choice or bad at portraying Mister Fantastic. But having Gruffudd return to the role would have worked so much better on numerous levels. Firstly, there is no expectation from fans for him to return to the role. While many fans viewed Krasinski's role in Multiverse of Madness as confirmation that he would reprise the role in the mainline MCU, that doesn't appear to be true. Casting Gruffudd would have ensured that such a misunderstanding would not have happened.
Secondly, the Fantastic Four films from 2005 and 2007 are not exactly the most beloved comic book movie adaptations. They got a very mixed reception at the time, which means that having Gruffudd return to the role, even briefly, could have been a redemption of sorts. It would have been similar to how Andrew Garfield returned to play Spider-Man in No Way Home.
Finally, it would have created a unity between the characters of the Earth-838 universe. While the Fox X-Men and Fantastic Four films never shared continuity, having both Gruffudd's Reed Richards and Patrick Stewart's Charles Xavier be part of the same alternate universe in the MCU would have created a sense of continuity. And it would have been able to do so without throwing reference after reference into fans' faces.
While Krasinski's role as Mister Fantastic works in Multiverse of Madness as it is, one can't help but wonder how things would have been had Gruffudd reprised his role. Even though those Fantastic Four films don't get remembered in the best light, there are those who grew up with them. And given how much Disney is catering to early 2000s nostalgia with Obi-Wan Kenobi and Tobey Maguire's Spider-Man in No Way Home, maybe Gruffudd would have been the perfect fit to play the character once again.
To see Krasinski's Mister Fantastic, Doctor Strange in the Multiverse of Madness is streaming now on Disney+.