no, they are not weak. but you must keep them properly adjusted, shock loading a loose chain will lead to failure. if you let them go too long on the xp it will wear your tensioner unevenly making it useless.
Yes chain tension is critical for longevity. Alot of peeps don't check them regularily because of the location of the adjuster bolt behind the muffler. That inside top spring can be a beeeotch.