Starlink will never replace 4G/5G in relatively-populated areas, because any RF wizardry they can do from orbit will work even better for talking to a tower at short range.
If you're in an area where it's not worth building cell towers, then Starlink will have plenty of bandwidth... but that's not where most people live.
When you look at a city from orbit, you see millions of radios all stacked on top of each other, screaming. That can never scale as well as a distributed array of towers.