Their flaw was to whittle away the extremely large reserve (30 Divisions!) on propping up even point in the line under pressure. When Guderians ill-advised breakthrough occurred it should have been smashed, but the French had basically nothing left in reserve.
Hence we all learnt the wrong lessons about tanks.....
Agree about the reserve, you even get the impression, that a WWI French General Staff would have done WWII much better than the WWII one.
Panzergruppen would have been of no use on the French side, and although mobile Armycorps were present and with huge potential for operational counterattack the French CCC system was was too slow reacting to utilise them.
But if you let all French staffs at say regimental level and above be equipped with reliable radios - and capable of using them - the campaign will end up very differently - no matter how the French tanks are deployed initially.
BTW I don't think the lesson of concentrating your tanks was wrong by 1940, it proved the obvious way to outmanoeuvre a slow reacting army re-fighting WWI. Already by June 40 however the French had sensed how to counter it (360 degree fortified positions in chequerboard formation as oppsed to a WWI like continious frontline) and by mid and late WWII these principles had been implemented to a degree meaning that tanks had to be accompanied by an ever growing component of infantry, artillery, engineers etc.
Regards
Steffen Redbeard