I would say that since the idea apparently started with Lucas and he specifically stated it was done to prevent bidding wars because they simply couldn't afford it at the time supports the thought.
I don't think it was the sole intention. But two things stand out to me that was part of the deal. The fact that the HR departments would inform each other if their employees were applying for a job at a company within the group; which by the way should be considered a huge privacy issue. Also that when an employee was made an offer, they only received a "final offer" to specifically avoid a bidding war. Those two things directly relate to wage suppression to me.
As for your example, that's quite true. But in the end it still stifles those employees' ability to increase their income because these companies directly conspired to not recruit from each other. It is not in the employee's interest to worry over if Company A wants to give them a pile of money to simply leave Company B but not work. Two companies coming to such an agreement for their benefit is a detriment to the employee, which is what the lawsuit is about.
Never mind the fact that the whole thing is clearly illegal under multiple federal and state laws. Therefore, their intentions are irrelevant.