oooo- everything I read says to watch the parade in frontier land because that is where the parade starts. After the parade it is easier to exit as the parade winds its way through the park-
Is Frontier land a not so good place to view the parade?
Or people leaving during the parade is what causes the mess?
Well, now, that used to be the case. However, The Powers That Be have decided to reverse the direction of the CaDCT parade a month or so ago, so now it starts on Main Street and ends in Frontierland. Now, there's always a hoard of guests that follow the parade... and when it ended on Main Street, most would simply exit the park. Now they find themselves in Frontierland... at a Dead End.
To say the crowds are darn near unmanageable is rather an understatement.
I'd suggest watching it on Main Street in the future.
Does the train run during the parade? I'm thinking that it doesn't...but maybe I am remembering Disney Land and not Disney World...
The WDW Railroad doesn't really run during the parade. Well, they sort-of do, but there are delays while the floats cross the tracks at Frontierland.
So Sorry

....I think you should let Disney know about this experience maybe they should be monitoring the crowd level there during parades!
I can assure you that Disney is constantly monitoring crowd levels --
especially during parades. Higher attendance numbers result in a reduced number of show stops.
They encouraged people along the stone-wall path and the wooden walkway to keep moving but a lot of people ignored the poor CM's and stopped to watch the parade. So the people in the back just kept pushing forward while the people in front were blocked by people who had stopped to watch the parade. It seems like Disney does know about the problem and has tried crowd control measures but some in the crowd just weren't paying attention.
You pretty much nailed it. The simple fact of the matter is that there are some Guests who have a sense of entitlement and think they can sit (or stand, or park)
anywhere in order to see a parade, regardless of others. It's unfortunate, but there's not much Disney can do about it (especially if they willfully ignore CM requests to move) -- by the time Security arrives the parade is over and the Guests have left.