The variables involved in any crash make generalizations about gear difficult--see opinions of Nexo/Velocity gear on this forum. Some like it, others not.
Beyond the leather type/design/production you have sweat, rain, putting on/pulling off weakens the gloves over time.
I had one (pricey) pair of Dainese gloves wear through the palm in less than 4 months, the other is still holding up. I've had zippers fail and velcro wear without serious use on jackets/pants/boots/back protectors too.
I've come to the conclusion that gear is a bit like insurance--it may not cover you when the blubber hits the road, but it's better than nothing, so ride accordingly. A global database of crashes and gear worn (with damage) might help zero in on what works but we still only have anecdote for the moment.