It seems the only thing this mod is generating is the Ender Ore, so that is what I have now disabled.

Googled a bit around, found a good thread explaining it:
https://www.reddit.com/r/feedthebeast/comments/5x0twz/investigating_extreme_worldgen_lag/

Proposal:
Expand upon WorldGenMineable instead of implementing the IWorldGenerator interface and go from there, as stated in the Reddit post.

what version of the mod are you using?

2.2.1-Hotfix.

I noticed there's a new version, 2.2.3, but the changelog interestingly enough doesn't mention anything in regards to this.
Neither is your source code up-to-date so I could've checked in advance.

fixed in latest release.