Thing is, the Constitution pretty much locked the Regency council. The Regent could not change the constitution, nor name new grand dignitaries (who were members of the Council) or grand officers, such as new marshall. Eliminating Napoleon's brothers using a legal loophole is pretty much the maximum the regent can do. This is why Berthier is so essential in 1811 : he is the only marshall with a seat in the Regency. Of course, these limitations would be scrapped in time - the empire cannot work unchanged for 18 years - but not in 1811, when stability - or appearance of - is tantamount.I don't think he would have issue subordinating himself to Davout. He knew he wasn't a great battlefield Marshal, and that was his best role. Napoleon sorely missed Berthier in the Waterloo campaign, which is why I think it would be a mistake to keep him in Paris. If you needed a marshal of good reputation in Paris- you had several choices- Kellermann being the best choice here.
I believe it was Soult who had Berthier's role during Waterloo, my guess is he would have gotten the nod here, and Suchet might have taken the lead in Spain (the Spanish ulcer will be more of a thing in this scenario too)
Suchet was a good commander, but no Wellington. Also much depends on how much time France has before a new war- the less time the more likely marshals stay where they are at.
Also, the GDoW, why not concede it to Austria instead of Russia if you absolutely had to?
Also, wasn't Massena disgraced by 1811? You can always be rehabilitated, but he saw no action after 1809.
For Massena it depends of the date of the PoD, before or after may 1811. I'd rather had him on the field. Either way, as the important members are all partisan of a Bourbon solution in Spain, Ferdinand VII comeback is very likely. No one is arguing for Joseph...