Cheap middlemen, the British held their dominance by being cheap...expensive middlemen get cut out, which is precisely what would happen to the British Merchant Marine in the latter half of the 20th century. Thus if Britain loses its marine then European and by extension global trade suffers too.
Ditto the loss of cheap British finance...
Ditto the loss of cheap British manufactured goods...
Likely European business and industry is retarded by the fall of Britain. France mind won't care because France will be reaping the benefits and while it might lose on an absolute scale the French are only going to notice they are doing better than all of the other losers.
Like you suggest Antwerp may well become a port comparable with a depressed London, still neither combined will likely amount to the London that was.
Overall Europe is poorer but France might be richer. Given past performances however it is quite likely to squander its advantages. The Germanies might well rise later in this scenario but in time they will probably rise and if the British do not recover then there will be no one to bail the French out when they do.
So ultimately I suppose German wankers (speaking technically to their AH styles not their personality/habits) will be the big winners but the French should get to strut for decades possibly even an entire century.
Britain loses big time here.
I maintain the expensive middleman. What you are forgetting is that Britain's power in the late 18th century was was largely founded not on peaceful free trade but on violently established mercantilist monopoly.
Britain did not like fait competition. Britain user its military naval power to kill competitors and establish quasi-monopolies. And those quasi-monopolies, especially the one on India, enabled Britain to make huge profits and to accumulate huge amounts of capital.