Of the 3x links ttaskmaster supplied in post #33 2x are about CLC problems. As for numbers of people with problems, there are considerably more threads/posts of of CLC problems and failures than there are of upper level air cooing in cases with good airflow.
As for longevity, even CLCs with 5 year warranty is only 1/2 or 1/3rd the potential life of a good air cooler with only the cost of replacing fan/s and maybe a mount update. I'm running a Thermalright Ultima 90 and a Ultra 120 (4x heatpipe) installed early 2007 that have only had fans and mount updates.
You are lumping CLCs into same group as AIOs that are not CLC. Again, there are 2 kinds of AIOs, CLCs are the majority of all AIOs buy more a 10:1 ratio, maybe a 100:1 ratio. CLCs are also the most problematic. There are threads of users who have had problems, same as there are threads/posts of users who have gone from CLCs to top tier air.
I would venture to guess that most CLC owners have little to no experience with top tier air coolers, nor do they understand the importance of proper case airflow. They saw the advertising hype of CLCs as water cooling and though of CLCs as budget custom loops and rushed out to get one, so when they post up about how great their CLC is, how it dropped their temps 10c and how much quieter it is, the comparison is of a case with poor airflow using cooler supplied with CPU .. a worst case situation. In most cases changing a stock case with stock CPU cooler to a CLC automatically adds 2x more fans to the case that came stock with 1x or 2x fans so have doubled or tripled case airflow by adding CLC.
Owners of cases with good airflow and upper level air cooling don't even consider about buying CLCs.
Most custom loop components are way better quality than AIOs and CLCs. CLCs are the absolute cheapest and poorest quality liquid cooling made. AIOs are better, but only as good as low end custom loop components.
Depending on what case, motherboard and RAM you have you could get a top tier air cooler and couple of case fans for less money, cooling as good or better, less noise potential and much more dependable than AIOs/CLCs. If you are interested start a thread and we can help you sort it out.