You are confusing levels of description.
"Free Will" is a social and psychological
concept which has essential significance in a network of human behaviorial concepts like "responsibility", "self", "culpability" etc. If you doubt this, consider the social result of removing "culpability" from the language !
"Determinism" is a mode of argument primarily supported by successful prediction of limited physical
events. Philosophers having failed to give a clear definition of "causality" prompted Kant to conclude it was a perceptual a priori
(i.e a wired in mode of thinking). Causality has no place in modern physics partially because the time dimension within which it seems to operate has been subsumed as an aspect of "space-time" and can no longer be considered to be an independent reference frame.
Thus the argument that physical events are deterministic and that they are a necessary substrate for cognitive events is flawed on at least three counts.
1. Determinism/causality, despite its limited success in predicting what we tautologically call "mechanistic behavior" is ultimately a cognitive concept.
2. Necessity does not imply sufficiency.
3. "Events" are observer defined by selection of the boundaries of the event window.