AVR with servos are slow acting. it takes seconds before the wiper move between the coil. Surges happens in milliseconds.

Still the best protection for overvoltages are MOV(MEtal Oxide Varistors) they clamp at nanoseconds speed. Couple that with gas-discharge fuse and it will clamp more current. Most UPS have this built in that is why they are recommended for electronic appliances than AVRs. Online UPS are the best protection u could get, inverters are ON all the time voltage gets conditioned all the time.