basically a brake that causes this much hassle bleeding, is a bad brake.
To butcher the old adage; powerful, light, simple, pick any two. The higher end Shimano brakes are expected to be light and powerful. The Servo-Wave levers help with this by increasing the leverage ratio after the dead throw is taken up. Problem is, this magnifies the problem of any air in the system.
Trying to miniaturize the levers and calipers probably also resulted in the transfer ports not being optimized for bleeding. Thing is, they aren’t impossible to bleed, they are just a bit tricky and need some care. As long as trained mechanics can successfully bleed them, Shimano have made an acceptable product. It’s not possible for companies to guarantee that their products are completely user-serviceable.
On top of that, Shimano have made millions of sets of brakes over the years. It’s inevitable that there will be a lot of users with problems if you sell huge volumes of any product. The users who don’t have any issues don’t post about it on web forums so it’s impossible to judge the proportion of users that have experienced problems.