I will try to answer the best I can in my own words on why I think it is better, I can not prove it or disprove it. The modification information from SP8XXN and SP5XMU mention the board is a Doherty amplifier. In reading up on these amps (wiki style) one device is switched on in class AB and the other is basically class C and off, needing a high peak level to switch it on, as it is used for the high peak to average transmissions of UMTS.
The article I read also said that power is lost as the input power is split two ways into each device by a 90 degree phase shift with different lengths of track, so in my mind half the input power is being diverted to a device that will not amplify any signal until it reaches it's designed peak switch on point. I have no idea at what level this is!
So to me, to get back this wasted input drive the second device needs to be biased as the first, in a class AB mode.
Now as it was designed for around 2100 MHz the 90 degree phase shift is not going to be 90 at 2400Mhz as the tracks are longer then required, but any phase shift change on the input is being reversed on the output or close to it.
As to drive level, I know that my pre-driver starts to limits out at less than 2 Watts, I have also reports that others that have done the mods have achieved a very maximum of 120 plus watts for short periods and this is not something I would NOT recommend, I have taken mine to an excess of 90 watts before my nerve gave out.
There are others doing similar mods, in fact a James Smith posted on facebook and in in IO groups
James is probably the first that brought it to my attention followed by a local radio ham Tim G4WIM
Each has done it a slightly different way but end up with similar results. I have been to Tims's location and know his test gear is accurate. Do try and have a look at both links.
Do not expect to run the devices at full power and for them to last long also do not forget you need something like a peak to average difference of 6dB, but if you know that the peak output is say 80 watts that is 3dB better than saying the peak output is 40 watts and the average is 20 watts rather than 10 watts.
I hope this explains it from my perspective, it is probably the best I am capable of giving.