Charity sometimes has created a gravy train and rewarded those in senior positions too much but they also provide lower waged work for their employees.
Do wealthy philanthropists benefit in other ways other than avoiding tax, yes I think they do.
I think you need to examine the competing philosophies of individualism and collectivism and decide how this sits within democracy.
So if Mr.R.Banker gives £1m and doesn't pay tax he decides how his social contribution is spent, which may include remunerating top charity boss but also help to relieve poverty in the Sudan. He has the democratic power of individual choice to decide what social ills he relieves. He and his charity are not democratically accountable.
But if Mrs.livesonasandwhich pays all taxes due, she acts within a democratic system where politicians decide which social ills should be relieved. This is a collectivist model where those that decide where the revenues are spent are democratically accountable not just to MrsL but also to all of us collectively.
Of course the best way to relieve social ills is to create both a collectivist and fair society, the libertarian will always resort to individualism even if personal choice and freedom results in inequality. Why? because he knows he has something to gain.
Goerge Osborne wants a shrinking state, he isn't a collectivist but he has a huge black hole to fill, one I might add that was caused through tax avoidance of the richest, off shoring of assets and company profits, globalisation and the fact that the banks themselves advice their clients and also take part in these avoidance schemes. GS gives a great deal of pre-profit cash to charity, strangely mitigating against some of their other global abuses such as contributing to poverty in the third world.
My conclusion is it's part of the silent take over where all money, charity incl will be out of the hands of governments. Without the ability to control the cash flow, George et al will have the very smallest but also least democratically accountable government possible which will mean that the strings will be visible for all to see.