Paladins struggle more at greater levels not since they're unviable, but because more wow gold courses that can counter them get better. Others start gaining gap-closing abilities while the paladin remains comparatively the same speed. The largest problem for your paladin is a shaman.Shamans really are a pretty good counter to them with their Purge and Dispell skills. Paladins are still a course that is useful, just busted by comparison.
Warlocks at this level are similar to mages in that their strengths lie within their crowd-controlling. The majority of the 19 warlock's harm secondly from the Curse of Agony and will come from Corruption. The problem for these comes that their DoTs can be dispelled by priests with ease.
Life Tapping is harmful, as warlocks at this level do not have the survivability because their caster counterparts. Levels are due to more access to spells, naturally. However, a huge aspect to keep in mind is their dependence on soul shards. In regards to experience, 19 twinks don't have a great deal of leeways. It would be much too easy to unintentionally level the warlock into 20. A great player with appropriate team support could probably pull off some crazy tricks, but they aren't as inherently powerful as the others on this list.
The exact same cannot be said for shamans at lesser levels. They are strong healers however lack priests, paladins, and druids' survivability and utility. Shamans suffer cheap wow classic gold from the high mana prices of their totems and weaker DPS compared to their counterparts. Most lower-level battleground groups prefer priests and druids.