  Constructing a quantum computer requires immensely precise control over a
quantum system. A lack of precision is often quantified by gate-error metrics,
such as the average infidelity or the diamond distance. However, usually such
gate-error metrics are only considered for individual gates, and not the errors
that accumulate over consecutive gates. Furthermore, it is not well known how
susceptible the metrics are to the assumptions which make up the model. Here,
we investigate these issues using realistic simulation models of quantum
computers with flux-tunable transmons and coupling resonators. Our main
findings reveal that (1) gate-error metrics are indeed affected by the many
assumptions of the model, (2) consecutive gate errors do not accumulate
linearly, and (3) gate-error metrics are poor predictors for the performance of
consecutive gates. Additionally, we discuss a potential limitation in the
scalability of the studied device architecture.
