Obtaining a Russian visa is not a mere formality;
Yes, this is true.
However, Russia consulates seem to apply different standards worldwide. While some are very strict, some (esp. in Finland) are somewhat more accomodating. If you then add a competent and "connected" visa agency to the table, it should be quite easy. It worked for me twice for a Russian Visa, applied at the Russian embassy in Helsinki (I am not a Finnish citizen).
Now, if transit in BRU is entered they see this:
BRU was not a transit station for the OP. A one month stay in Schengen would not count as transit.
So once an agents reads what the system is telling him/her, he will insist on seeing a visa before letting you board.Common sense may tell them something else, but that is what they are trained to do.
I do understand the point, however, the airline cannot defend themselves by quoting TIMATIC. And again, I make the same point as NickB. The airline would not have been fined by Belgium, because there is no explicit onward ticket requirement.
VISITORS ARE REQUIRED TO HOLD PROOF OF SUFFICIENT FUNDS TO
COVER THEIR STAY AND DOCUMENTS REQUIRED FOR THEIR NEXT
DESTINATION
Well, a document does not have to be a ticket. A mere printed out online Visa application confirmation with a visa agency would suffice.