Drag on a siezed fan
I spent about fifteen years flying the 737 3/4/5 and never found the simulater to err in any performance respect
Even details, if an engine fell off the zero fuel weight went down by the appropriate amount
The sim aircraft performance suffered markedly with an engine failed with fan siezed at V1 but it was still within the climbout spec if the approved technique and speeds were followed but not if higher speeds were used