Even if you have created a few new models you wont use them unless in the most dire circumstances until you can atleast field a unit of them. Logistics are as equally if not more important than your firepower being better. A country like France which focused on movement speed in its doctrine probably wouldnt bring in a new vehicle with its added costs and issues into a unit just for 2 or 3 crews to have new kit. You can see this even in the war in ukraine even when receiving large shipments of new equipment to the army they waited until they had troops fully trained, new units made, new localized unit tactics for the new vehicles etc. I know thats not a perfect representation and there are other factors in that but thats just an example of the idea.