I don't think that engulfers are problem.
Yeah, engulfer as normal unit is fine in most cases. Issue goes in complex of kirko abilites.
@Tombles
1. Range. First of all, engulfers (as almost any flyer) have high survivability, can clear neutrals and level up very fast. Kirko doctrine +25% exp helps it further.
Prime Rank Engulfer is powerful unit with 8 range. Here comes first issue: engulfer range. To avoid coming of 10 range engulfers devs could change it prime rank - Shrug off, Critical, Morale. Range is most useful and powerful skill for flyer. Actually, other flyer hasn't it, except engulfer.
2. Psionic buffs. Main problem is that you can mass it on a lot of units (or even on entire battlefield in past). 'Guiding Aura' is right way, it's pretty tricky to use, but still possible to abuse on 7 units. 7 units with psi buffs. It can be mass Bio or Fire resistance, mass evasion, +3 shields and healing depends from wish or need of user. Or even 3 of them (!) simultaneously. And +2 to range on top. As for me, I'd delete such ability like you do with Compelling Presence. But it will be needed something in return, so I guess it's impossible.

3. Absorb Pain. As psionic buff it causes all issues described above and on top of that adds new ones. 35% dmg reduction is huge. Also it's even easier now to use it, because Absorb Pain has a cooldown now, shorter than time of effect. Yeah, it could be cancelled by Stagger, but Engulfer Mount has Stagger Res.
Okay, my bad. Sorry.