Arguably they do — both are important, and you’ll notice the effects of them both. At level 100, EVs can add 63 points to a stat compared to IVs with 31, but IVs can be maxed on every stat instead of only two with EVs. So you get more points overall from IVs, but they can’t affect individual stats as much as EVs. (IVs are what you are fixing by hyper training.)
In terms of the question, if you hyper train HP, Def and SpDef, you will definitely notice the difference.