I read this advice years ago and the more I play the more I think this is the best advice for trying to improve your tank rating.
If you have good supports that keep near you, tank is fun. If your moira is in their back line trying to be like tracer or sombras, tanking is misery.
To be fair Moira flanking and cleaning up kills is good, problem is if the other support is Zen (can’t heal even if he wants to), Lucio (do i need to explain), Mercy (busy sucking off some DPS in a back alley) you definitely won’t have fun.
A good Moira will time the flank well whereas a bad one won’t. Thing is there are a lot more bad ones but the few good ones I’ve played with seem to know when to stay with team and when to pursue kills.
Imo the time to go for a kill is when a squishy is weak and vulnerable.
My frustration is moira’s flanking on the first team fight of a game, when the enemy team is at full strength.