ECU ratings are based on an ancient x86 benchmark, and don't really compare well with each other anymore, let alone with totally different architectures. I think they've been trying to retire it for years.
I'm disappointed that they aren't retiring the vCPU designation, too. ARM doesn't have anything like hyperthreading, so an ARM vCPU seems to equal a complete core. The a1.xl has 4 cores, 4 threads. The m5.xl has 2 cores, 4 threads.
I'm disappointed that they aren't retiring the vCPU designation, too. ARM doesn't have anything like hyperthreading, so an ARM vCPU seems to equal a complete core. The a1.xl has 4 cores, 4 threads. The m5.xl has 2 cores, 4 threads.