I feel all the UK to BRU routes will suffer post Brexit. I'm aware that a reasonable about of traffic on those routes is people going to EU institutions on corporate fares. There's bound to be a question about whether that will be sustained in the future.
That said, properly marketed, BRU (and FRA and MUC) should be hubs to rival AMS. It just needs LH Group to market it well and with competitive fares. And work out what to do to encourage *A frequent fliers to use the route, even though BM isn't in *A.