Well, I think its almost entirely separate skills to create campaigns in the different tiers.This is "solution in search of a problem" thinking. D&D isn't a game that you "win" by getting to level 20. If WotC wants a campaign that goes to level 20, they should write one that has a compelling reason to go that high. Pulling the lever in the skinner box isn't what makes a TTRPG fun. If you can't write campaigns that make it fun to spend a year at levels 1 through 5, you're not going to be much fun if you zip through 20 levels in a year, either.
For levels 1-4, you almost have to design the game for babies because its so easy to unintentionally kill off a player through a bad dice roll even when you make it as fair and even as possible.
Yet from levels 17-20, a DM has to pull out all the stops. Wards are just as much a must as locks were at tier 1. Unpredictable environments and weird creatures are a mainstay. You can't plop down a cyclops on a bridge and call it a challenge anymore.