"substantial freedom" is correct and usable in written English.
You can use it to describe a situation in which someone has a lot of freedom to act, think, and make their own decisions. For example, "He was given substantial freedom to pursue his own interests."
The Dodd-Frank Act gave regulators substantial freedom to impose measures to strengthen the system on their own.
The new bill would continue to give the C.I.A. the substantial freedom it has long enjoyed, while the revisions to the Army Field Manual announced Wednesday would further restrict military interrogators.
Each state receives a lump sum of federal money, with substantial freedom to shape its welfare program, provided it requires work and sets time limits on the receipt of cash assistance.
The EU may be the embryo of a future federal state, if the union develops into an organization whose central government is capable of making decisions independently of the consent of member states, and particularly if it is given substantial freedom to act in the field of foreign and military policy.
But today's communist rulers have radically altered their views about religion and have granted substantial freedom to Christians prepared to worship within state-sanctioned churches.
Such nonlinear elimination, which we term particle enslavement, results in a nonlinear formulation with memory requirements comparable to those of a fluid computation, and affords us substantial freedom in regards to the particle orbit integrator.
The filmmakers also enjoyed substantial creative freedom, Mr. Michaels added, because of the movie's relatively small $10 million price tag.
MacFarlane granted Povenmire substantial creative freedom.
Creator Seth MacFarlane granted Povenmire substantial creative freedom.
Proteins are able to adsorb strongly to most surfaces, because they display a wide variety of functional groups (charged and uncharged, cationic and anionic, hydrophilic and hydrophobic) and because they exhibit substantial conformational freedom.
In particular, the Index noted that "[n]otwithstanding the country's outstanding performance in most categories, there are substantial limitations on freedom of speech and freedom of assembly, with Singapore in 49th and 60th place, respectively, out of all 66 countries".
