Team psychologist? It's a role that managers end up assuming, often for the worst. Unless you're the rock metal band Metallica, who actually use a team therapist, problems aren't usually sorted out other than by turning over staff, which Metallica can't do without destroying the cash cow.
No, I'm talking about consulting for the employee as a kind of ethical Machiavellian. Otherwise the interests don't align.
It may just be the examples this author gave that made me think of this. An initial temporary team where everyone is clearly less skilled than you are? Dear lord, feed them the answers so that they get credit for fixing the security issue. Everyone will then sing the praises of working with such a team player.
Work closely and non-combatively with the tech-lead to get a full picture of their knowledge and level of defensiveness. Then stay out of the tech-lead's way while you slowly begin building up a robust testing system. Make sure each pull request is short and easy to read. Space them out so you don't make a pile of work for your colleagues.
Pretty soon you'll have a bunch of allies, probably including the tech-lead. Or if the tech-lead is still defensive, you'll have a big, fortified wall of unit tests between the two of you. They'll be forced to argue with failed tests instead of with you directly, which is one of the few (and perhaps one of the only) benefits of technological progress.
It's good, but rare, to be irreplaceable.