In fact, it is pretty safe to say that any fight that you swap up an expertise trinket on, expertise is probably your worst stat anyway. Since you are likely to swap out expertise trinket for a stamina trinket. That means that the boss fight has considerable damage output / bursty damage output, any of which greatly favors mastery. So for those types of fights that you would swap out expertise trinket, expertise is your weakest stat anyway. (disregarding dodge, parry and crit ofc).
The only fight I actually used it for was for soloing chimaeron. (got the trolling-for-raid version)The healing from ji-kuns is a bit underwhelming though, you're right. I don't fall that low very often unless we're wiping. I guess I'll just keep it in my bank until there's some situation that calls for it... maybe some new chimaeron boss or something.