-Disadvantage for melee attacks in dim light conditions. In 5e, Only ranged attacks have disadvantage, dunno maybe the devs thought it was more balanced this way
Incorrect, In 5e, no attacks have disadvantage for dim light. Only perception checks do. Both ranged and melee attacks do have disadvantage if your opponent is heavily obscured however.
-Frightened creatures should only be able to dash away from the creature that frightened them. (Some frightened skellys continued to open sarcophagi in one of my runs)
Not true, the frightened condition states "you have disadvantage on ability checks and attack rolls while the source of your fear is within sight, and you can't willingmy move closer to the source of your fear".
However some sources of the frightened condition add additonal restrictions. E.g. turn undead reads: A turned creature must spend its turns trying to move as far away from you as it can, and it can't willingly move to a space within 30 feet of you. It also can't take Reactions. For its action, it can use only the Dash action or try to escape from an Effect that prevents it from moving.
Other than that I agree with you.
