In اِسْأَلْ and اِقْرَأْ, the initial joining hamzah supports pronunciation of the imperative; it is not an original root radical.
The hamzah of the root س أ ل is still the middle radical in اِسْأَلْ.
The hamzah of ق ر أ remains final in اِقْرَأْ.
By contrast, كُلْ has undergone a special dropping of the first radical hamzah. The three imperatives must not be forced under one identical deletion rule.
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Imperative Hamzat al-Waṣl Versus Radical Hamzah
Rules of Hamzated Forms: Lightening, Substitution, Elision and Short Paradigms
In اِسْأَلْ and اِقْرَأْ, the initial joining hamzah supports pronunciation of the imperative; it is not an original root radical.
The hamzah of the root س أ ل is still the middle radical in اِسْأَلْ.
The hamzah of ق ر أ remains final in اِقْرَأْ.
By contrast, كُلْ has undergone a special dropping of the first radical hamzah. The three imperatives must not be forced under one identical deletion rule.