How about,
Greatly increased range for counting allies within Coherency.
Something like a 100% or 200% increase. That way the Zealot can be quite far away from their team and still count as within range, but they can’t run off into the next postal code. They could even benefit from auras as well (even more incentive to generally stay close). They would still provide coherency to others at the usual range though.
AND,
The Zealot gains coherency with teammates who are dead.
If one teammate is dead, you will count as in 2 coherency no matter where you are, which will help a lot if the Zealot decides to charge/sneak ahead to rescue someone. That way it would still be useful for the clutch when you’re the last one standing, because you’d count as in 4 coherency. Could be capped at 2 if 4 is too much. And you don’t get dead teammates’ aura effects.
Maybe this could apply to the whole team, as in if someone is dead (besides the Zealot), everybody counts as in 2 coherency no matter where they are. Or maybe the Zealot provides greater coherency counts for each dead teammate, so if one person is dead, the Zealot counts as 2 people for everybody else’s coherency, so a team of 3 sticking together would count as 4. (Also possibly capped at 2. Maybe upped to 3 if two Zealots have this aura.) That way it doesn’t benefit only the Zealot.
It could be renamed to something like “Together in Spirit” or “Kinship” or “Brotherhood” or “Eternal Bond” to emphasize still being part of a team even when the team is further away, or dead, as opposed to “Loner.”