Yeah there were multiple times when the allies could have pushed Germany over before they started steamrolling. When they remilitarised the Rhineland, as you said when they occupied the Sudetenland, and even when they invaded Poland.
France started pushing into Germany once war was first declared and there was basically nothing in front of them. Most of the tanks etc were in Poland. If they had continued pushing then it might have all ended there. Instead they pulled back to the Maginot line and the rest is history.