We going offtopic here.But i cant say there is a weakest class atm but instead its better to say abit harder to play and perform well.So if I have to name I would go with tos and hox, both are really strong and games changing only in only few people hands like ofr example Zarkane or Vouga while the majority cant do anything while playing them.On the other hand on demo with other dps classes like necro,sin,barb etc.... even if you cant play these classes at all and you are a strawman you can still manage to kill some stuff due to range or op dps.
Demo is pretty easy to make kills even if you dont know what you are doing but I could name only a few that actually know how to play the class, like Dodge for example.Keybinds,instants,breaking line of sight,be aware of what is happening around,keeping an eye of enemy immunities,know when to push and when to pull back,use your cc's to protect your team,never being stationary etc...
After playing for years necro I can say I have alot more fun playing pvp with demo atm due to as I said to the previous post the mobility of the class.So to the guy who opened the thread I would advised to keep playing pvp on demo until you bypass the learning curve because in the end it worth it.