Millions is an intense exaggeration, the bomb was under a lot of water, and lets be honest, you've seen left over ruins from the Hiroshima bombing, yes? There were even survivors (until radiation got 'em. >_>😉 Mercer was far from point blank, and the bomb being under water still managed to liquify him with force.
The closest standing building is over 150m from ground zero, and one of very few things to be still standing, the Prototype one was 5x that. Alex was around <200m from the centre so he was still in the ground zero area. Only survivors were ones far from the impact zone, anyone in within 20-50/100 miles was vaporized.
Alex gets the claws out to win imo