For what N&W needed, it was perfect. It really depends on what you're wanting to do with it. Bogies help spread weight.
Lead bogie can spread weight and also help guidance at high speeds.
Trailing bogie can allow a deep, wide firebox, for better power at high speeds.
Taller drivers are easier to balance at speed, and also determines the speed where peak HP comes along. (Of course, N&W figured out how to balance J class's small (for a 4-8-4) 70" drivers for 100mph running)
Actual tonnage a train can move is determined by tractive effort, which is limited by the amount of weight on the drivers, especially on grades.
So if you want to move a train on flat ground, at high speed, then "super power" locos are perfect for you.
But if you want to move the absolute maximum the train can can, especially if it's at low speeds and/or on a mountainous region, you may want to focus more of the maximum weight on drivers. As noted in >>1595065
the 2-6-6-6, the heaviest loco ever built, had a tractive effort of only 110,000lb, which is absolutely pathetic compared to the Y6s 126k compound/166k simple, the Big Boy's 136k, or the VGN 2-10-10-2s 147k compound/176k simple.
But I would say the Y6b was the most advanced mallet, and probably was the best one built. Though you could argue for the N&W 2-6-6-4s and Challngers as well, provided you used them in the correct manner.