Good to hear from you again B T.
As usual, you seem to have summed up the situation accurately. Air France is reducing a lot of its short haul European destination frequencies and BRS is due to see fewer flights next summer, so that might help a bit but in itself wouldn't be the tipping point.
Don't forget that BHX is just up the road too with LH to FRA and MUC amongst its German portfolio.
When LH (Eurowings) operated BRS-FRA April 2008-April 2009 the route was building well enough (99,000 passengers in that period) but then came the deep recession and LH decided that FRA from LHR, BHX and BRS was too much of a good thing. BRS was the newest route of the three and the least developed, and doubtless the one with the least potential especially in such straitened times so it was the obvious one to go. Had the recession not occurred BRS-FRA might well have survived but that can be said about numerous routes from airports around most of the globe. I know that you are familiar (at first hand) with the recent BRS-FRA situation but others might not be.
It may well be then that if BRS is to see an expansion into Germany in the forseeable future the best that might be hoped for is a point to point route. It's not to be sneezed at but it would clearly be of much less value than a LH one into FRA with onward connections.