By "slippage" I mean the ratios of the input and output speeds not corresponding with the mechanical position of the tapered pulleys, i.e. the CVT tapered-pulley mechanism is set for (say) 2:1 reduction but the input is spinning 3 times the output with the balance taken up by the surface speed at the pulley having a substantial difference to the surface speed of the belt. *That* is "slippage", and that does not happen (aside from perhaps a minuscule and negligible percentage) by design in any normal CVT. It *will* happen if someone fills the transmission with the wrong fluid, such as normal ATF instead of the special CVT traction fluid that they're supposed to use. The whole CVT mechanism operates in an oil bath, and it's a special fluid that's meant for this application (and using the wrong fluid, such as normal ATF, WILL blow up a CVT).
The "slip" up or down the pulleys (not tangential slippage as described above) between the tapered pulleys only happens in conjunction with the whole assembly rotating while changing ratio. (Belt-type CVT mechanisms cannot change ratio at a standstill!) If you actually calculate the amount that each element of the chain ("belt") moves with each revolution while it's changing ratios ... it's insignificant and may actually be accommodated by the inherent deflection of the chain assembly (which is designed to flex slightly). Bear in mind that the clutches inside a normal automatic transmission "slip" with every gear change, so it's not like a normal transmission is completely free of wear points, either.
I'm not entirely sure what your point is. Are some production CVTs unreliable? Oh yes; there have been more than their share of bad ones. Are there some reliable ones? Absolutely; most of the newer ones seem to be pretty good for their intended applications. And you can say EXACTLY the same thing about conventional stepped-ratio automatic transmissions. Some are good, others are explode-o-matics. Honda built a whole design generation of bad 5-speed automatic transmissions attached to V6 engines around the turn of the millennium give or take a couple years. The Volkswagen 01M has a host of designed-in flaws. Chrysler had enormous difficulties with Ultradrive (a.k.a. the A604/41TE, their first electronically-controlled 4-speed auto-box). Yet the 41TE morphed into the 62TE, which after a few initial minor teething troubles, has mostly been OK. Biggest problem ... People filling the transmission with the wrong fluid! That transmission wants Mopar ATF+4, not Dexron.
Some CVTs are bad. Some are good. Some conventional-design automatics are bad. Some are good. Heck, some conventional-design MANUAL transmissions are bad. Some are good. What's your point?