Spring Break saw busier DME times, but generally speaking, wait times have been relatively normal. We waited maybe 20 minutes in total on our October trip. The average time between landing and arriving at your resort is 90 minutes using DME, and I think that still holds true, with the exception of particularly busy times like Spring Break, Christmas, etc.
Buses to and from the parks were fine in my experience, with the exception of rope drop. Its not uncommon to have to wait for the next bus because they fill up much faster than before. We used Uber when trying to make rope drop, but used the buses the rest of the time and it was fine.
All of this said, I would not rent a car unless you need it for other reasons. IMO, any potential delays you may experience are minimal enough where the additional cost of the rental car and parking would not be worth it.