Many ambiguities exist because every country knows better than another and files 'differences'. These can easily become quite dangerous and the 'climb/descend via' can help to reduce these problems.
As an example: imagine in the UK there is an SID with a 3000B restriction on it. ATC clears you to climb to FL 90. You can now ignore the 3000' restriction unless ATC restate the requirement. Now we go to the USA where a similar SID exists and ATC tell you to climb to 9000'. This time you'd better not ignore the 3000B unless ATC tells you you're unrestricted.
I've obviously over-simplified things but it is easy to see where individual countries' differences can cause a problem; especially when you're on the back of the clock and can't remember if country A does it this way, while country B does it another.
Climb via the SID is easy to understand. 'Climb' is easy to understand. I don't see where the problems are.