Ty, I think this is a good question. Abrasive damage, pinhole punctures (by thorns), and tears are different kinds of failures, and the degree to which a fabric is susceptible to each kind of failure depends on a combination of fiber properties (material, orientation, etc.), denier, weave, and coating.
But you don't need to know all of those characteristics of every available pad in order to make a reasonable comparison. If you want to use an inflatable pad and you want better durability than your Synmat UL7, I would suggest considering some of the variants that have a higher denier surface fabric. I think your reasoning seems correct. The heavier fabric should be much less likely to tear. And if you know you will be camping in an area that abounds in sharp rocks and thorns, bring a thin foam mat to put underneath.