SN Brussels Airlines used to havea two weekly flight to St Petersburg with an Avro on Tuesday and Saterday if I remember correctly.
The new SN still offers these flights, but from September on, no more flights show up in booking. Sometimes only saturday show up.
Will St Petersburg be only served 1x a week by the new airline?
A 1x weekly flight (and no direct competition between these cities) seem to be a little low.

My next question is about the service. The old business class is only offered on European flights to Moskow and Helsinki and to Tel aviv.

Does that mean that St Petersburg will have the flex / light classes? What about Cassablanca? Quite far to be offered without a snack.