Eh, if the tanks hadn't started, France probably would have held. The tank charge through the Argonne forest at near road-speeds caught the French seriously off guard, as their plan involved reinforcing Belgium at the river, holding the Maginot line, and dealing with a force comprised of only light infantry in the forest. Without tanks to rush the lightly-defended gap, France might well have had time to deploy their reserves to reinforce the Argonne and held the Germans off.

They get a lot of shit for losing quickly, but if German tank development had been 10 years behind the curve, they would've been victorious.

Also of note, the invasion of Poland was not nearly as successful as historians would have you believe. If only Germany had invaded, it would've been hard fighting.