Bottom line is if you shoot any rifle enough it will need adjustment or replacement of the rifle, in particle if the builder made mistakes in material and/or construction. Case in point several years ago I was looking for reasonable accurate scopes bolt action rifle and tried another Spring Field Armory M1A but had issues (have had 13 SA firearms and none could ever shoot 200 rounds with out failing due to soft materials, design / parts tolerance etc. even after trips back or to a smith), an Armslite AR10 (was during the era when they had rough chambers and the hammer failed, it is gone now also), a DSA medium heavy barreled FAL (worked great for a friend but extractor and spring had to be changed once, it is still around but did not get scoped yet) and an HK91 (had to clean it once after shooting a lot in cold weather .... its still around 30 years later). Of all the rifles the HK 91 shot the best, the DSA FAL is close but has not been scoped (late in the cycle) and the other two (plus several other M1As since ... all which failed) did not group as well and thus are long gone. For accurate scope rifle shooting, have moved back to bolt guns, where anything much over 3/8 inch MOA is broke (PSS and TRG42 being favorites along with friends DTs)
I have 30 thousand plus rounds through one SP89 (MP5K-PDW) on full and not even close to having to change a roller, figure at this rate it will be several hundred thousand rounds, before have to change to the next over sized rollers. Friends have tens of thousands of rounds through 308 HKs, which were shot hard to the point of melting the silver solder (not failure just little balls ... and was on semi ;-) with out changing rollers yet, once they do need to change rollers one can get over size rollers in several different increase sizes, then changed the locking piece and and lastly change the barrel or set it back if the rifling is still good and start the process over again. Some of the hammer forged barrels have had a very good life in the rifle calibers, so the story goes.
If a clone is built with the wrong bolt gap to start or another issue due to incorrect construction, then one can have issues, but that is true with any firearm system (reference my issues with SA and Armalite). Looks like you need to do a little more research on what bolt gap is, on going issues and corrective actions, before writing off a system or possible you just stopped by for the debate and increasing posting count ;-). For reading would get the Book Full Circle and do some searches here.
PTR Construction Issues
http://www.hkpro.com/forum/hk-clone...012-another-ptr-91f-diminishing-bolt-gap.html
http://www.hkpro.com/forum/hk-clone-talk/153650-new-ptr-91f-breaking-bolt-gap.html
http://www.hkpro.com/forum/hk-clone-talk/145901-newbie-ptr-91-problem.html
Century C93 Construction Issues
http://www.hkpro.com/forum/hk-clone-talk/155759-question-c93-bolt-gap.html
http://www.hkpro.com/forum/hk-clone-talk/149693-century-c93-bolt-gap-what-do.html
http://www.hkpro.com/forum/hk-clone...-back-ghillie-but-looks-good-before-hand.html
If you get a German HK94 or one of the high end "MP5" clones from some of the regulars you should be all set to go. The issues with bolt gap is more of an issue with the clone builder than a "design issue"