because he introduced the spoils system which turned political appointments into patronage rather than merit.
It's not like appointments were made on merit before him. It's just that the circle of patronage was much smaller. Jackson widened the circle. Real meritocracy at the Federal level was half a century away at that point.
He made mistakes such as getting rid of the Bank of United States
No.
People need to understand this: The Second Bank was not a benign, technocratic institution like the modern Federal Reserve System. It was a political actor with policy preferences and the power and influence to pursue those preferences. Nicholas Biddle happily used the wealth and power of the Bank to influence elections and elected officials. He did so in a way that was not only corrupt, but contrary to the wishes of the broader population. Killing the Bank was one of the best things Jackson did.
That nothing worthwhile replaced it isn't his fault: There was literally no conception of a modern central banking system in the proto-economic science of the time period for him to draw on. The very concept didn't exist anywhere else. The national banks in Europe were
not modern central banks, either, mostly being fiscal agents of their respective governments rather than managers of the money supply charged with economic stability. That was
also something half a century or more away.