Not really. I remember the AT to ATX transition in 1995, and it definitely didn't fix the parts issue. Your motherboard and power supply would fit. Anything else could still be a problem.
You still had pick the right CPU, memory, and expansion cards. Early ATX motherboards had ISA, PCI, AGP. It did nothing to fix most of the parts issues. I build PCs both with older AT and ATX standards. ATX did fix the "IO card" problem, but it wasn't a panacea for all PC building.
