OB1
Jedi Master
Well Robert Downey Jr wasn't a big name when he launched Iron Man, he was a washed up 80s actor. Iron Man made him a Big Name.It's not just being in a franchise, it's what you did, and how recent/hot the franchise is. Michelle Rodriguez is primarily known for the Furious films, but not as a lead. In terms of large franchises, Pine is known as a lead for the rebooted Star Trek films, which are a second tier franchise, and for a co-starring (but not really) role in the Wonder Woman films. Pine would be a significant lead, but at the same time he's not Duane Johnson, Robert Downey Jr., etc. Hugh Grant has had a stellar career but folks who go to this sort of film aren't going because they need to see Hugh Grant.
There's big names and there's Big Names. None of these are names that move the dial a ton when it comes to opening weekend box office. In Hollywood terms, they aren't that bankable (truly bankable stars are a short list).
The thing is, outside of Tom Cruise, there aren't really bankable actors anymore (look at how Black Adam performed with the Rock starring). That said, having recognizable names in a new franchise can help (like RDj did with Iron Man), and Pine, Rodriguez, Grant and even Sophia Lilas are that. They don't drive the box office for people who aren't otherwise interested in the film, but they give a kind of reassurance that the film has some people who are Hollywood regulars as a kind of seal of approval.
I wonder how many Trek fans there are compared to D&D fans? The reboot had a solid $75M opening ($375 Worldwide total). Or how many Captain America fans there were prior to 2011 (also a $75M open and $385 Worldwide total)?
And I can't overstate this point enough, if the prognosticators are thinking that D&D is male centric, they haven't been paying attention to the trends over the last 8 years. My wife now runs a bi-weekly game that consists of 7 women and 2 men, and the ladies are already planning on all going to see the film when it comes out. If that's too anecdotal, take a look at Crit Role fandom. Pine, Grant and Rodriguez are all popular with female moviegoers, and the trailers all show women kicking butt.
I don't know that D&D will get to a $75M opening, but I'd place a serious bet that it opens over $40M.