London to Berlin sleeper rail service from May 2023
theguardian.com
theguardian.com
So unfortunately, EasyJet is still much cheaper.
London to Brussels is only 2 hours, so ideally you'd want a train arriving at Brussels at about 19:00. With the current timetable, the train from London arrives at 18:05, which is hardly ideal.
(However, I don't see any promotion of the connection to London on the website.)