Purists may knock Mercedes-AMG’s entry-level—and mushrooming—range of “43” models for watering down the brand, as they lack the hand-built engines and mad power output of AMGs with numerically higher badges. Yet even Affalterbach’s modest fettling has produced some impressive vehicles, such as the Porsche Macan–baiting GLC43 crossover and the comparison-test-winning E43 sedan. With much of the latter’s on-road goodness stuffed …