Your question as if pulled out of context.
All altcoins are different. How can you talk about the shortcomings of all at once? Each of them has its advantages and disadvantages.
1. Lack of anonymity. Almost all transactions can be traced, however some altcoins are created to solve this problem. There are additional methods of encryption.
2. Very complex and expensive mining. This is a drawback. But, not all altcoins can be mined. Some projects are developing a super-computer to speed up the processing of data.
And so you can continue to infinity. I think you need to adjust your question in a narrower sense.