Is it permissible for a student to obtain a higher diploma in computer science without attending classes, knowing that success is guaranteed whether he attends or not, for the purpose of completing his university studies with it, given that he possesses sufficient experience in this field?

The purpose of formation/training is to gain experience, and what you mentioned about everyone succeeding without gaining experience is a big mistake. If the distance learning system does not contradict the regulations in force in your country and your computer proficiency is as you described, then there is no objection to you benefiting from the certificate granted under the legal conditions.