The funny thing about RAW vs. RAI is that anyone can read RAW since it’s written right there for all to read. But only someone like Jeremy Crawford can tell us RAI, since he worked on the design of the rules.
For Magic Missiles, I disagree with his RAW because the Damage Rolls section on page 196 of the PHB seems to be referring to multiple targets of a single AOE spell, not multiple missiles/bolts/arrows striking one or more targets. But I agree with his assessment of the RAI, which I can’t really argue against even if I wanted to.
ETA: I guess, technically, MM does deal damage to “more than one target at the same time,” but then the passage goes on to give Fireball and Flame Strike as examples.