If you can get 100k+ out of a stock or LUK throwout bearing/slave cylinder (which is pretty likely) then why would a company build an alternative?
Nobody would buy it. I sure as hell wouldn't and I have two trucks with M5ODs! LUK parts last a long, long time. They fail just as often as other "good" parts do. Everything fails. I had a brand new $800 iPhone dead right out of the box at work, does that make iPhones pieces of shit too?
I'm sorry you had a parts failure. It happens. I have replaced a ton of M5OD slave cylinders and can tell you that they do not fail more often parts made back in the good old days or whatever. They are also SIGNIFICANTLY easier to replace than similar parts on other vehicles... Rangers, Explorers, B2's are just really easy to work on, I can do a clutch job in a night after work.
In summary: there are no upgraded parts and the factory style ones are just fine regardless of how many people complain about them. You are just not hearing the 98% of us who have no issues.