I think the negative feedback on this is an over reaction. But whatever.
Keep the "good for a group" aspect. Keep the defensive aspect. Thematically temp hp makes sense as it goes along with radiant forcefield and ablative armor. But it could just as easily be a group/aura effect that works like a radiant forcefield, and give everyone a 15% damage reduction effect for 3 seconds every 2 seconds for 20 seconds. That still requires everyone to remain near the artificer (or vice versa) for the 20 seconds to benefit for the full time period. Leave the cooldown at 2 or 3 minutes.
Or what about a kind of effect that "converts" damage for the 20 seconds. Characters under the effect of the aura would on hit gain temp hp equal to the (real) damage they just took. So if I have 1000 hp, and get hit for 300, my new hp is 700, but the aura generates 300 temp hp. Now if I take another hit for 500, that ate 300 temp hp and 200 real hp, so it only generates 200 temp hp, leaving me at 500 hp + 200 temp hp. Maybe flavor it up by only allowing the aura to absorb/generate from physical damage, not spell damage. Maybe this isn't an aura anymore but an area of effect buff like an sla. Note how - without other real healing - this could only possibly grant a character up to their same number of real hp, because only loss of real hp is converted into temp hp. That's way weaker than the warlock for a single person but on the other hand can apply to the entire party for 20 seconds every 2 or 3 minutes. So there's a balance there and you keep the value up when in a group.