Of course they are that good, so long as you get modern devices, not the old versions such as the
IRF610 and such (which are hopeless by modern standards - people still sell them though).
Discrete MOSFETs use vertical current flow and have extremely low Rds(on) values (1 to 20 milliohms for
lower voltage devices is the sort of range). With vertical current flow all MOSFETs on the die must
share the drain terminal, which isn't useful.
MOSFETs integrated onto chips (such as the A4988) are DMOS which have lateral current flow
and much higher on-resistances (0.2ohms being the lowest I've seen, 0.3 to 0.6 ohms is typical).
Thus H-bridges for more than an amp or two need to use discrete MOSFETs or you'll need big heatsink /
forced-air cooling on the chip. The current goes through 2 devices so the power dissipation = 2 I^2 R
If you do use a discrete MOSFETs its normal to use all n-channel devices and bootstrapped high-side
drivers - n-channel MOSFETS have lower on-resistance due to increased carrier mobility of electrons
compared to holes (which carry the current in a p-MOS device).
Where MOSFETs fall down is on the sensitivity of the gate to feedback currents via the gate-drain
capacitance - the higher the voltage and current being switched the more careful you have to be
with the gate-drive to keep things under control. For voltages above about 100V these days everyone
uses IGBTs which are far more robust.
[ My current project uses MOSFETs rated at 200A, 400A peak.