Well.....
They are better than jeans and a jacket.
But IMHO, youse gets what youse pays for. Bear in mind that the leather on most all motorcycle specific leather suits holds up pretty comparably with respect tear strength of the leather or abrasion resistance. The difference is that the more expensive suits (gloves are the same in this respect) are constructed better, and, this is the key point, won't blow open when you crash. The Vance and Hines factory roadracing riders in '89 or '90 learned this when they went with Fieldsheer leathers as a team sponsor of leathers (ever see them around anymore...I don't think so...) and found they were blowing apart on them in a light crash. With a better suit you get better construction, better armor, fit, etc. Look for top-stitched seams everywhere, not just in places, well positioned and designed armor, double leather over the fanny, hip pads, etc. Talk to suit mfrs. (e.g. Helimot or Vanson), and ask them what makes a good suit. Learn to recognize a good suit when you see one from its construction.
A Dainese T-age, for example, has literally no seams on any exterior aspect of the suit, its all one piece of leather...all the seams are on the inside aspect of the suit, e.g. inside of the arm, thigh, etc., so there is no seam to blow open on the outside of the elbow, for example, if you were to crash and slide. Also, the quality of armor in that suit is unparalleled.
If I wanted to get a quality, one-piece suit for roughly $850 (which, like a mountain bike, is about the minimum you can spend and get something that is truly worth your investment), I would stay away from Frank Thomas, Joe Rocket, and Teknic, and look instead at Texport, SYED, Tiger Angel, or Spyke.
I have been impressed with the quality of those suits, and I look at suits very carefully at the vendors when I see them. I have also been impressed with the AGV suits made in Italy, which are also reasonably priced (not the AGV ones made in the Far East).
The best suits I have seen at the higher price points are Vanson, Dainese, Kushitani, Nankai, Spidi, Alpinestars, and RS Taichi.
As far as the development of armor, uses of different materials for protection, design, etc, etc, Dainese has consistently been the most innovative and aggressive with the development of safety equipment (for example, they invented the back protector). They have an incredible R&D investment and department (called D-TEC) that is constantly working on improving the safety of their suits and related safety equipment.