I've worked for big, medium and small charities. Some are badly run, yes, some are incredible. You just need to do your research rather than writing them all off. Look at who their CEOs are, how many staff they have. They are all so different.
Also be mindful that big fancy offices might be subsidised or even free, given as a gift from a donor etc.
And being a volunteer is all well and good but you need a paid volunteer manager to ensure people are trained properly, made to feel valued and that clients are safeguarded. And yes, they will need a salary.
But as someone said upthread, a big number of charities are there to fill in the gaps for services the government doesn't provide. Womens refuges, refugee organisations, homeless orgs. If everyone stopped giving to these organisations, there would be very little support for some of societies most vulnerable people.
So no, I won't stop giving to charity. But I will do my due diligence as to where I send my money, just like I do with who I but my clothes from, or where I get my food shopping.