Hindenburg despised Hitler, and did everything he could to stop him, but he pretty much had no choice. Like most, he figured Hitler wouldn't last long.
Your point about having a monarch over "democracy", I do agree with 100%. Just as it was wise to keep Hirohito after WWII.
‘Democracies’ are forced to compromise on things that should not be compromised. People choose their poisons, or have it imposed on them.