I was there for ATM, and I'm so freaking glad it lost. It's a prime example of "a camel is a horse designed by committee". A 53 byte cell with a 48 byte payload? Of course! What an excellent idea! We definitely want a 10% overhead on a ludicrously small packet, just so it has tolerable voice latencies if you scale it down to run on a 64Kb DS0, never mind that literally everything in the industry was scaling up to fatter pipes.

ATM was nifty if you had a requirement of establishing voice-style, i.e. billable, connections. No thanks. It was an interesting technology but hopelessly hobbled by the desire to emulate a voice call that fit into a standard invoice line.