The RMV Tickets, the Hessenticket and Deutschland-Ticket all cover the same travel equipment, whether inside or outside of Wiesbaden, in their respective areas of coverage.
A 75-minute radius does not tell us where you are going, and there are many places you CANNOT go within such a radius if you opt to go with RMV tickets. A simple train ride north along the Rhine to St Goarshausen (50 minutes) on a RMV or Hessenticket would take you outside the RMV and not be covered without additional ticketing.
As for RMV pricing: Example: A day ticket for Wiesbaden-Frankfurt round trip (45-50 minutes) is priced at €22; a week-long ticket for the same route is €66. More distant destinations may cost more for each type of ticket.
The D-Ticket (€58) makes this complicated travel area very simple. It will get you from FRA airport to Wiesbaden in the first place (assuming you fly into FRA.) It has zero additional costs no matter how many days you use it or where you choose to travel. As long as you are using it within the month of April, the Deutschland-Ticket (€58) is clearly the most versatile option and the clear choice, IMO. Even if your stay includes a day or two in May, which would require additional ticketing, a D-Ticket for April would make sense to me.