  The velocities of the quasiparticles that form Cooper pairs in a
superconductor are revealed by the upper critical magnetic field. Here we use
this property to assess superconductivity in magic-angle twisted bilayer
graphene (MATBG), which has been observed over a range of moir\'e band filling,
twist angle, and screening environment conditions. We find that for pairing
mechanisms that are unrelated to correlations within the MATBG flat bands,
minima in an average Fermi velocity $v_F^* \equiv k_B T_c \ell_c /\hbar $,
where $\ell_c$ is the magnetic length at the critical perpendicular magnetic
field, are always coincident with transition temperature maxima. Both extrema
occur near flat-band van Hove singularities. Since no such association is
present in MATBG experimental data, we conclude that electronic correlations
that yield a band-filling-dependent pairing glue must play a crucial role in
MATBG superconductivity.
