Depends what you mean by hard?
The older games tend to have shorter ball times, does that make them hard?
There isn't a Bally/Williams I haven't got to the wizard mode on.
I've got to wizard mode on virtually all Sterns I have owned - including TWD (LMS),LotR, AcDC,
BDK, JP, GZ, AIQ, SM, TSPP, FG, etc.
I was very close on IMdn but didn't quite get there before selling it. But sure I would get there now with flipper cooling fans.
The Sterns I was furthest away from wizard mode were PotC and WPT, both need lots achieving and if you mess up on a mb it gets harder to requalify and attempt again. I've never seen ANYONE get to Gauntlet on PotC.
I've only had limited time on Woz and DI from JJP, but was only 1 shot away from wizard mode on both. PotC doesn't even have a wizard mode, but the mini wizards are incredibly difficult, especially considering the effort to get there, and then once you do limited instructions on what you're meant to do.
Some wizard modes you achieve by default just by having long games (GZ), others you have to target specific tasks (
BDK).
It really all comes down to your definition of hard.