> The second disadvantage is a lower efficiency than with permanent magnets, which cannot be improved so much as to match PM motors, because the electrical currents that circulate through the rotor windings must generate heat. The lower efficiency also makes cooling more difficult.

It depends.

With PM motors if you exceed the Curie temperature, the magnets lose their magnetism. Also one can control the rotor excitation current on EESMs so core saturation is less of an issue compared to PMSMs.

The brushes are also quite long lasting and easy to change on a good design so maintenance is not as a big of an issue.

ASMs are even more robust but they have lower power density and efficiency but are better for coasting.

There is also the SynRM which uses an unwound rotor with flux barriers (cutouts) that aligns with the stator flux, no magnets needed. It's basically as robust as the ASM but without its lower efficiency disadvantages and also no brushes, at the cost of more complex power electronics and lower speed noise.