The drop information on Wowhead should still be fairly accurate (barring any actual bugs when they added level scaling.) They didn’t change what mobs drop what.
Your skinning level itself will affect drops, but only if you’re skinning is below the level needed to get the mobs “true” drop. In that case you’ll get a lower tier of leather. (Being above the level doesn’t affect it.)
The reality is that this has always been a pain for as long as I remember. Hides just have a low drop rate. Just keep working on the mobs that give medium leather regularly. (Off the top of my head I’m thinking Southern Barrens or Stonetalon Mountains.) I’d also check the AH regularly for cheap hides, and it may be worth it to try some other recipes that don’t use the hides, even if they are less efficient overall.