Every enemy from past games included in BoTW has undergone some changes - seeing what new elements could be incorporated into their designs should be reasons for pursuing them, not marks against them.
The Helmasaur idea above is a good example - to go on further with the Redead example, they could be riddled with arrows or have weapons lodged in their bodies that drop when defeated. Poes have already been conceptualised with scythes in Twilight Princess, and the Poe-like floating Guardians in Skyward Sword demonstrated a variant which would work with twin blades. Deku Babas already drop usable sticks in the N64 games, something similar with a variety of wooden weapons could be incorporated here. The pincers of Gohmas or Moldarachs could easily be incorporated as droppable weapons. Lynels didn't originally have weapons at all.
And as shown by the Talus, the incentives can also come in the form of other kinds of item drops.
Even with the existing ones shown in the series so far, there's plenty of space for a wider variety of enemies - entirely new designs would offer even more freedom.