This game was intended to have two mage classes at release.

Both happened to have at least:
1 type of heal spell
1 type of revival spell
1 type of nuke
THM got debuff abilities
THM got offensive drain and siphon abilities
CON got debuff removal abilities.
CON got defensive abilities.

It had already been established that the balancing was improperly implemented at launch, and did not make significant improvements until 1.18. Neither mage class at the time were dedicated healing classes by your measure, merely classes that happened to be capable of healing. The classes were better balanced to reflect their story backgrounds at 1.18, and will be nearly fully rebalanced at 1.20 .

And suffice to say, both will continue to be capable of healing. All that changes is the fact that the heal spell both classes use will be known as "Cure".