Ultimately, the answer to this question will differ from person to person because it will be based on personal preference. That being said, in the yoga community, cork yoga blocks are rarely viewed as being too soft. In fact, in some cases, you might find that some yoga practitioners actually consider cork yoga blocks to be too hard.
As a result of this, some people will choose to make use of alternative yoga blocks or simply forgo using one altogether. This is largely due to people being unaccustomed to using cork yoga blocks (or just yoga blocks in general). Keep in mind that the more you practice with a cork yoga block, the more you get used to it being a part of your routine.