And that design started all the way back in 1937. And had so many problems and delays, less than 500 were built...
The 1937 date really is misleading. The VK 3001 (H), 3601 (H), 4501 (H) and Tiger II are so different in design or even intended use that they were pretty much restarting from scratch at every iteration. 3001 was just initially meant to be an uparmored BW (Pz IV's class), which became a potential alternative to the Pz IV. 3601 was to be an adaptation of the design to have more armor and a 105mm howitzer then salvaged to get a high velocity 75 instead, but it had to use a completely new powertrain and a vastly revised hull and turret shape.
4501 is the first tank really designed for high penetration tank busting/breakthrough and has yet more mods, and development only started in early/mid 1941, and Tiger II dev only started in late 41/1942, and even then lost its old roots altogether as the hull was instead unified in design with the Panther, thus actually inheriting from a different family.
Thus 2 years of development is actually quite fine for such a big endeavor. And when you account for all the pre-1942 developments I mentionned and what had been done for other German tank families, and what had gone to the drawing stage before being cancelled in 42-44, the reality is that Germany actually developped new designs every 2 years on average, and that for sometimes 3 families simultaneously. Germany's failure to introduce new chassis has more to do with changing requirements/priorities than actual inabilities, and when you look at the neverending story of extremely similar "new Pz IV" chassis proposed in 4 years, they could easily have just picked one of the earlier offers.