I am intrigued by the Splines wear. It seems reasonable to assume that the TRENT is a well balanced and smooth running machine. I also think it possible to entertain other than lack of lubrication as a partial factor in the loss of Spline metal.
Under the great stress of Climb thrust, the engine is reliant on its internal balance for long service life.
Splines, though accomplishing a "Rigid" coupling, are subject to vibration (chaotic) and Harmonic (synchronous). Each wave upsets the face of Spline, Groove with opposite and energetic input. Hence the loss of metal from the "Crest" of the Spline, and the faces as well.
Under its ultimate Power loading, any impact that impinges on the face/groove of the Rigid coupling produces wear. Almost all of the Thrust from nozzle and Fan are used to propel the a/c, some is lost as friction, it is friction that may have done in the Rigid coupling. The "Tug O' War" between LPT and Fan is "Refereed" at the Thrust Bearing, any load impinges on the Splines, if there is very rapid loading/unloading in this couple, the joint beats itself into the wear rate that caused the AD's IMO
I still think that while very important, the oiling is not the entire answer. It may be that the extra one tonne of max Thrust is a bit too much for the system. That is a very big Supersonic Fan, any vibration and harmonic whether mechanical or 'acoustic' is a very big load.
Just some thoughts
bearfoil