Your experience does not represent the norm... the reputation for Simplex derailleurs being what they are is well earned.

Have you been using those derailleurs for 40 years ?

Do admit that I like them when they work, am not so fond of them when the jockey wheels crack and pull the derailleur into the spokes and the number of bikes I have seen with replacements to their original Simplex is an indication that many failures came early.

Lucien Juy's perverse affection for plastic killed Simplex which was once one of the most successful component makers on earth when they came to their senses it was too late as Shimano and Suntour had taken over dominant positions in the market.