If you are talking about regular EC2 (not T series, or Lambda, or Fargate etc.) you get the same performance (within say 5%) of the underlying hardware. If you're using a core, it's not shared with another user. The pricing validates this...the "metal" version of a server on AWS is the same price as the full regular EC2 version.
In fact, you can even get a small discount with the -flex series, if you're willing to compromise slightly. (Small discount for 100% of performance 95% of the time).
This seems pretty wild to me. Are you saying that I can submit instructions to the CPU and they will not be interleaved and the registers will not be swapped-out with instructions from other EC2 virtual server applications running on the same physical machine?
In fact, you can even get a small discount with the -flex series, if you're willing to compromise slightly. (Small discount for 100% of performance 95% of the time).