Meh, i don't think at that point that Dunkirk was even remotely close to holding out for another week. Those troops there weren't orderly retreating anymore they were fleeing the theater headlong.
And we are not talking about a negligible amount of British Soldiers. We are talking about 300,000 of them, at that point thats 1/3rd of the British Army. Thats a crippling blow and would definetly remove Britain from any offensive actions or even directly supporting the French for quite a long time.
Now your argument would stand if we would assume that all those troops around dunkirk had historically abandoned the siege of the city while the airforce continued bombing the town but fact is that those troops sat around for the entire siege around teh city doing exactly fuck all besides sieging it. THey were not fighting the french as you say above but were siegeing the city until finally the last of the british had fled.
Now if they would have moved in with their tanks the time period the siege had taken (i think it was a week?) would have been severly shorter and the french would have had even less time to recover, adding to that the 300.000 losses to the british that would have been more successful than what happened historically.
As for the African Theatre, i will concede the point, i would have to read up on that at the moment and would propably only find that you are right