After the campaign Hitler ordered a considerable increase in the number of panzer and motorized infantry divisions. The number of panzer divisions was soon doubled, through this involved a halving of the tank strength of each division. Thus the German army, though doubling its nominal strength in armored divisions, did not acquire double the number of tanks, which was after all what counted.
Source: Panzer Leader, p138
So the idea is that in order to create more mobile divisions, quickly, the stupid Hitler ordered half the tanks to be taken from the existing units thus weakening them.
France May 1940
Number of Panzer Divisions: 10
Number of Panzer Regiments: 16 – All units have two except 6,7,8,9 Panzer divisions.
Number of tanks with Panzer Divisions: 2,582 – 258 per div
Operation Barbarossa 1941
Number of Panzer Divisions: 17
Number of Panzer Regiments : 17 – One per Division
Number of tanks with Panzer Divisions: 3,266 – 192 per div
Total AFV strength for Barbarossa was : 3,266 tanks in Pz Div plus 250 stugIII plus 135 Panzerjager I plus 340? tanks in four Panzer Abteilung = ~ 4,000
So what happened was that indeed units lost a Panzer regiment but this did not necessarily mean that strength was affected by 50% . If we look at the compositions of the tank force the difference is even more striking.
In France tanks that are incapable of frontline service (the Pz I and Pz II) constitute 57% of the tank force.
In operation Barbarossa the same types constitute only 27%.
In summer 1941 Germany has not only more Panzer divisions than she did a year ago but they are vastly better equipped. The only downside, compared to 1940, is that each unit has 25% less tanks.
Guderian was exaggerating . Because he was a legendary soldier he gets off with a warning.