> and at that time the prevailing wisdom was to never buy a pre-built

That's still the case, and always will be — with a pre-built you're at the very least paying for someone to assemble it for you, so it's always going to be more expensive as a baseline.

Beyond that, the chance they've chosen good components and haven't tried to screw you over on less flashy ones like the motherboard and power supply is low.

That's not to say it's literally impossible to ever find a good deal. You very well might have. Doesn't change anything though.