So then Lester's disqualification should be Zimmerman's slam dunk free one.,
Yes. Lester is limited in the terms of rebuttal. He cannot attack the factual basis, and has to rule simply whether the motion is legally sufficient, or not. If it is, he MUST disqualify himself.
If he doesn't disqualify himself, O'Mara will certainly appeal the ruling, and then Lester will get to be wrong for not disqualifying himself, and also disqualified - for bias.
If the next judge is as much of a biased simpleton as Lester, O'Mara's pretty much stuck with the judge, but can preserve errors for appeal.
The trial judge doesn't have as much "free" rope as he thinks he has. Lots of what trial judges get away with in on the basis of knowing the offended party won't appeal.