Personally think Jonathan fits best as a Berserker, and while I do get what you were going for with Joestar's Requiem, the fact that living (?) Joestars are summoned as well as part of it isn't the greatest. Also, I feel Jonathan's parameters would be rather high for a Servant of his relative youth.

I really like this crossover

This story just feel lazy and anti climatic.

Do another One shot. This time with Highschool DxD.

Ah, DIO is so DIO here.

Useless? It should be Muda