Running some numbers on the Morning Star change:
Tower of Giants Gigas: needs 222 ATK to OHKO
----Level 1 AA Luci starts with 419. Yeah.
Sacred Mt. Bakkes Brachys: needs 376 ATK to OHKO
Castle of Satan Voice: needs 379 ATK to OHKO
Castle of Satan Vampire Lord: needs 1072 ATK to OHKO, or 537 ATK to 2HKO
----two level 15 AA, which isn't that far-fetched because friend leaders exist, or a single level 70 SoD
Tower of Flare Ifrit: needs 179 ATK to OHKO
Polar Night Tower Leviathan: needs 934 ATK to OHKO
----max-level +0 AA leaves it with 19144 HP. This should be easy to combo away since Leviathan has no defense.
Tower of Nature Fafnir: needs 846 ATK to OHKO
----max-level +0 AA leaves it with 1553 HP. Actually has defense but still this should be easy.
Tomb of the Saint - Deep Hades: needs 1222 ATK to *2*HKO
----don't most people suggest to run with an Odin friend here anyway if you don't have a burst lead?
----two max-level +0 SoD leaves him with 6100 HP
Fertile Land Fortoytops: needs 386 ATK to OHKO
Ice Maze Megalodran: needs 741 ATK to OHKO
----level 39 +0 AA
Blazing Highway Flare Drall: needs 637 ATK to OHKO
----level 27 +0 AA
Twilight Woods Drawn Joker: has Flash Bind (but if you have levels this should not be a problem), needs 1215 ATK to OHKO or 608 ATK to 2HKO
----two level 24 +0 AA
COSITA Echidna: needs 1073 ATK to OHKO or 538 ATK to 2HKO
COSITA Fog Chimera: needs just slightly less than Echidna
----the Flame Chimera doesn't do enough damage on its own for the binds to be an issue, especially since at this point things really should be at least evolved once
COSITA Vampire Lord: needs 1396 ATK to OHKO or 699 ATK to 2HKO
----wouldn't you focus on the Pierdras first, though?
----two level 34 +0 AA
Do some of these take a bit more effort to kill with Morning Star? Yes. Is it alarmingly high amounts of effort? Not particularly.
Will run some other dungeons' numbers in another post if people want to see them.