Hi Eddy!
Stricktly speaking the term "there is always a horse in barrier 1" is not exactly true. "There is always a horse in the barrier closest to the rail" is the term I would use. Many times you will see barrier one empty. But I completely agree with your and KV's comments about the importance of barrier positions.
It is highly overrated.
Everything being equal it should make a difference.
But it rarely does.
The only time I take the Jockey into account is when the horse is starting from a wide barrier, a good jockey can minimise the disadvantage to almost nothing while a bad one can make it ten times worse.

Also a horse can miss the start from any barrier!
That's worse than a wide barrier.

As a matter of fact if there was any barrier I would avoid, it would be #1.
How many times did you see the fav boxed in?
Too much money lost on barrier one.