Stockholm actually does the splitting fairly well on ALL of their subway lines, and even their commuter lines have several splits.
You really have to watch each train at each station to make sure you're on the right number, just as you would a bus number.
Having said that, their suburbs are in small, spread-out pockets, so having splits only makes sense.
And also, for a city with almost EXACTLY the same population, they're putting our transit to shame
(except for the 2.4M suburban population outside of City limits)
https://www.transitmap.net/stockholm-rail/#jp-carousel-5453