How many Harry Potter films? Or Hunger Games? or Twilight?
Strong financial evidence that connected movies will sell tickets, with the right context. In the non-'rona world, anyway. Counter-example: John Carter, which was effectively killed by poor marketing and lack of an existing fanbase.
there are practical differences between connected movies and multi-part movies.
while I am generally in the camp of "the longer the better" - and to be honest, at lot of failed or mediocre epic movies in the past could have been enormously improved just by spending more time while keeping the same cast, crew and production value - the question is if a story can be split enough to give them the time but not too much to avoid piecemeal movies that can't stand alone.
If you don't want to release the movies back to back, which is more a straight to video thing, each has to have some usable structure to make them work on their own, which is a challenge when trying to keep close to the source material.
For example with Lord of the Rings, a relative successful example of a story split, a lot of the changes from the books involved moving stuff around or cutting it outright to give each movie workable arcs and pacing.
