The problem is that line of thinking only scales to when things work using the very basic level of abstraction presented. A 150W audio amplifier is a surprisin

The problem is that line of thinking only scales to when things work using the very basic level of abstraction presented. A 150W audio amplifier is a surprisingly difficult thing to get working right, even with an off the shelf IC. You have to consider grounding, trace impedances, current density, power supply quality, filtering and parasitics really otherwise you end up with wildly oscillating nightmares or exploding amplifier ICs.