> such motors require frequent maintenance for changing the brushes.

"Frequent" is all relative.

The Renault Zoe, 10y ago, was already using a synchronous engine with wired rotor. And most were going over 150kkm without any issues nor brush changes.

> because the electrical currents that circulate through the rotor windings must generate heat

Currently stator heat in wired synchronous engine is less a problem than in SynRMs with permanent magnets.

Most neodymium based permanent magnets start to be irreversibly damaged id they heat up beyond 100°C. That's currently why Tesla has such a good cooling system in their engine.

Wired rotor are bunch of copper coil, as such they are much more resistant to temperature gradients.