Most of it comes down to what it actually possible with the "official" ability system made by Mythic compared to some of the stuff the ROR team implemented server side. Stored within the client is a database which also functions as a set of instructions on how every single ability should work, defines how things can be modified, what checks can be made, etc. That DB is used by the client for some client side bits but it's also the same DB that was used by the Mythic servers to actually implement the abilities. The works and instructions of that database have now been reverse engineered and it's strengths and limitations are now known.
Some bits the old ROR server ability system could do are not possible with Mythic's system, but there's also a bunch of stuff in Mythic's DB that the ROR server can now do.
Sadly the type of turret buffs on the old ROR server code were not something that was supported so for now the Engi and Magus are taking a hit. Just remember that not all of the changes made are the final balance changes and the big balance patches using the new ability system are being worked on.
