TreeChopper appears to have logic to make chopping big trees slower than little ones, probably to avoid making going after Giant Jungle trees or Dark Oak trees overpowered.

Under normal circumstances (single player, or multiplayer on a server that supports TreeChopper) this works very well.

But, if you have TreeChopper installed in your profile (for your single player world) and you go play on a server that does not support TreeChopper then TreeChopper makes chopping Jungle and Dark Oak blocks unreasonably slow, worse than when you go after obsidian with an unenchanted pick.

The proper behavior when playing on a server that does not support TreeChopper should be "vanilla behavior".