There is a toggle between "static" (old) and "dynamic" (new) flying, si it's optional.
Just do realise the old system cannot do everything the new can, such as going thrice as fast or maneuver quickly enough, so expect to run into limitations on that.
Things like larger maps will pose no noticeable issue to the likely grand majority of the people that will use the "superior" (faster) system, and you can expect to lose out on things like i.e. rares, gathering nodes and treasures simply by virtue of being slower.
So it's optional, but there is a logical and silent "but" involved.
Plus it may ultimately end up replacing static flying in content going forward, depending on the level of adoption. Simply because it would no longer be worth the effort to facilitate it in design and such, wasting time and resources.