but care must be taken to take over manually very fast where LVPs are not in force
This is the key statement.
The actual case showed that it might be very difficult to react on such deviations in "poor" weather (slightly above Cat I). They didn't have enough visual cues to determine that they where off the center line until it was too late. Otherwise they surely would have disconnected.
A minimum weather for practise approach is a no brainer in my opinion. If you don't agree, walk along the skidmarks in MUC...