The debate of leather vs "ballistic nylon" goes on & on. Bottom line, either one will fare much better than plain ordinary cotton jeans. And though leather is the preferred material, Ballistic Nylon riding gear has come a long way. Not too long ago, when testing was done, leather was found to be better due to the fact that the bonding that holds it together is random matrix at more or less a cellular micro-level"...having much less tendancy to tear, along a lay of fabric sewn threads and smooth finish allowed it to "slide further down the road, preserving integrity of suit and ride. But and over time, leather can degrade and if not taken care of, dries out losing it's reliability and tear resistant qualities.
That said, though most of the advantages still favor leather, convenience, quality and price all factor in for the level of protection. For the equivalent price you can buy pretty good fabric riding gear and certainly much better than the equivalent "cheaply made" light guage leather faux riding gear so common nowadays. You can pretty much judge the quality of the leather by the thickness and even surface grain finish. It should be stiff when niew, if thin or extremely soft, concrete or tarmac will scuff, dig in and tear it in short order.
Just be selective, as the very middle to high priced fabric motor clothes can offer a decent amount of protection for the average rider and nowadays some moto clothing looklike jeans and such are very well constructed w/ Kevlar panels, double reinforced areas and even room for CE rated padding in key areas to protect the rider and worthy of a good look.