Of course you can not fly a true raw data rnav departure, but you can fly a non-FD manual rnav departure of course, even in MUC or FRA although if that is a good idea is somewhat different question. By the way, visual departures are still normal and every day used procedures in MUC, just listen in on clearance delivery instead of using CPDLC clearance.
And yes, low vis might not be the right place to fly raw data approaches, but to be honest, how many true low vis situations per year does a normal pilot encounter? Besides, manually flown CAT III approaches are a normal procedure as well, just not raw data.
But there are more than enough chances for any pilot to train his flying skills on the line in good conditions. both weather and traffic wise.