These are quite good, I must not have read the last iteration of them. They seem to not cover everything that was originally pull requested, but the operations that they do cover and what currently actually works seems to be more or less the same set, which happens to be sufficiently well defined in my opinion.
Therefore a complete revert is unnecessary.
To answer the other questions, it was not any one thing but a combination of incomprehensible code written to no spec and with no documentation (which was my opinion at the time, proven incorrect). As there in fact is a reasonable spec and documentation the code can be fixed.
I filed http://tracker.phpbb.com/browse/PHPBB3-10955 to start on improving the code. This was one of the points I raised in the original PR.