So many skills, but that's now been corrected. Definitely didn't change the outcome. For clarity, the latest version we have for the actual HP regen barrier is +HP when the party member does damage to another target. That is the only "regen barrier" for a Mystic. "Vampiric Barrier" was being used to describe the barrier that was stealing HP and turning it into MP(buy tera gold) which is actually Essence Leech and requires two different spells cast.
That is an interesting comparison with regard to spells that directly heal Mystics. They just have 3 and the targetable HOT doesn't target them. So, that'd leave two: orb + Sanctuary where they have to deal damage to get healed. Neither of those are actually "convenient" in that they have prerequisites of picking up orbs and/or doing damage. There is very early footage of a Mystic having a very large(Tera Gold), direct self-heal, but that's since been removed. We would love to see that same mechanic added back.
To be fair, the base damage stats for Mystics are the same as Priests in Tera. Given the +Attack buff for Mystics occurs very early on, not sure when the Priest +Attack Blessing occurs, but it's definitely later on, Mystics do appear to perform better and have stronger overall damage than Priests. Though, honestly, it's not by a very large margin at all. Also, you can easily stack +Tera online Gold Attack Enchantment Crystals and increase your overall Attack by a good bit. The support classes aren't supposed to be DPSers, but at least for soloing it's not horrible like in many other games.