The whole point of formal verification is to remove the necessity of understanding most of the work. We only need to trust the formalization of the problem statement, the proof verifier, and the formalization of the result. We already have proof verifiers that humans understand to a high level, and the formalizations of the problem statement and the result are much simpler than the full proof.
I'm confident that the Navier-Stokes equations can blow up because I'm confident that Lean works correctly, and I'm confident that the mathematicians verified the problem statement and result correctly. This is despite the actual proof not being human verified yet (as far as I know), and despite the "human-readable" version not actually corresponding to the formal proof. The formal method still worked.