They are COMPLETELY and TOTALLY DIFFERENT games! One has tanks and vehicles and ammunition from the 1940s and the other has tanks and vehicles and ammunition from the 2000s. That is over SIXTY years of developments!
The tactics (maneuver to get a flank shot) are very different thanks to the anti-tank missiles. In MBT you can hit stuff from much greater distances (LOS permitting).
MBT is set in 1987, but can be used for any cold war fight up to 1996/7. And why would you not want MBT unless you dislike the cold war period, if you like Panzer I bet you anything you will like MBT, and when the BAOR and FRG modules come out it will add so much more.