I don't know, I've got packs with both kinds of pull. I like forward pull better but it's never been an issue to get the belt cinched down with side pull.
But there is always "good enough" design, and "excellent" design... a forward pull is plainly a better design, and it's silly to go backwards from it.
And it's far and away easier with a forward pull if you have shoulder issues.
I still occasionally use a side pull from the packs in my "collection" and am always amazed how much easier a forward pull is to use, especially with an 80lb load.