That does not work. If I roll the check as is, the result will be higher than fits my character. Either you are removing my character by forcing them to pass a check they should fail OR I am reinventing Str/Dex in order to have the mechanics of the check accurately reflect my nimble waif.
It is okay to admit that merging Str/Dex means not being allowed to have characters with mechanical differences between Str/Dex unless they undo the merge by reinventing Str/Dex.
There are pros and cons to merging/splitting attributes. We can recognize both.