Ah, but there's a difference between being a great leader and a great money man.
Tilton was great at getting United back on track financially; if Goodwin or his successor (Creighton) had stayed at the helm much longer, there likely would not be a United Airlines. He's made a lot of changes at the top levels of United; mostly for the better in terms of financial performance.
I do not think that current United management is incompetent (just look at how much money they extracted from the rank and file employees

); they're just evil, heartless grinches. They do not have the ability/skill to rally the troops and inspire them to do a great job.
UAL management = great money managers, horrible leaders.
CAL management are much better leaders, which is why they're not willing to cede control of CAL's employees to UAL management. After reading about how CAL rebuffed DAL, I can tell you that I'd much rather work for a management team that views loyalty as a two way street.
You are correct that mergers are painful for the rank and file. Just witness all of the gnashing of teeth on this thread over the rumor of a merge.
As far as United's employees getting the shaft if CAL management took over, that's speculation on your part. I think that CAL management is able to look beyond the next quarter and realizes that an AMR/TWA-style merge would not bode well for the company in the long term.