If a modder writes things correctly, then there is no functional difference between the two. As DeferredRegistry is just a proper implementation of using ObjectHolders and Register event.
DeferredRegister was literally created as a helper for people who can't get it around their head to NOT statically initialize things. So it moves the thing that is bad to statically initialize {the registry objects} to the Register event behind the scenes. That's it. It's nothing special.
By "minor tweak" you mean "Major re-write of the entire loading system of both Mods and Vanilla itself."
Lucky for you, that was actually done in 1.13, which is one of the many reasons why we did the major re-write. So update to a supported version and you can have this cool feature!
Nothing in the log shows a crash of any kind... It just stops at 83%... Only thing we can tell you is to try stripping out mods and seef i you can find the one silently killing things.