First of all, if there were no dark matter (DM), you wouldn't ask this question, since structures — including galaxies, stars, planets, and you — wouldn't have had the time to form in the early Universe before it had expanded too much for gravitational collapse to occur. But let's use magic and make the galaxies anyway:

1. The power spectrum of the CMB shows that the total density of mass/energy in the Universe is extremely close to the critical density. That is, $\Omega_\mathrm{tot} = 1$. If there were no DM, then $\Omega_\mathrm{tot}$ just wouldn't be $1$, but rather $\Omega_\mathrm{tot} - \Omega_\mathrm{DM} \simeq 0.74$.

2. Similarly, if there were no DM, we wouldn't observe the same relation between supernova magnitudes and redshifts from which we infer the presence of dark energy (DE). Instead, the magnitudes would be somewhat *higher*, showing us that that expansion accelerated even faster.