Suggestion itself is somewhat reasonable, but killing example 'normal' teleport omni bosse's it's easy and doesn't take too long to kill it.
But then we are going for 'Hard' one's which are on teleport one's, as you said it does say, 'Better chance at rare drop's' also what 'hard' ones drop it's purely non-broken item's + can't compare teleport bosse's to lesser one's. Since they do drop broken item part's and not only those but: Olympos bond's, Supreme & Ultra boxe's as for normal teleport bosse's they do not drop ultra's or supreme's or any bond's either which is reasonable.
Hard mode bosse's are quite easy to kill still even thought they are taking longer than 'easy' one's, but can be more rewarding after getting drop on low kc.
Here's example from 'Hard' one's which were dropped today