In reality there is very little difference between creating money (reserves) and creating bonds. The notion that private market discipline stops profligate government spending by limiting the issuance of bonds by treasury is proven false by two things:
Firstly if push comes to shove the Fed would never refuse to honour a Treasury payment and secondly that the bid to cover ratios in bond auctions always indicate a higher demand for bonds than the self imposed/legislated constraints of congress would allow.
So the real constraint on spending is legislation, we could just as easily legislate full employment instead of legislating a balanced budget target.
You're mixing up the fiscal - Treasury, bond auctions, taxes, deficit, debt service - with monetary - central bank, interest rates, reserve requirements, QE.
The Treasury doesn't have the authority to create money [0], and the Government has to pad its balance sheet with debt.
The central bank on the other hand doesn't have this requirement. (They have the dual mandate to keep PCE at 2% and keep unemployment low [at NAIRU].)
Of course this is "simply" a giant technicality, but people find it useful. (Bond auctions function as an important signaling mechanism. Also credit default swaps issued for sovereign debt, and their secondary market is a kind of useful indicator. Plus the swaps, and the interbank "overnight reverse-repos for reserves" themselves are useful instruments for managing/handling/pricing-in/reifying risk.)
Again, you're right that theoretically anytime someone says "i owe you" they are creating money. And you can run a local bank easily with a spreadsheet and a large initial equity (as criminals oft do).
[0] this might not be true technically, as they might be able to mint coins without Congressional approval and need for appropriations (and hence collecting taxes or issuing debt), but the Fed still has to buy the coins so it's again the Fed that's creating the monetary base for the coin ... ¯\_(ツ)_/¯ - https://en.wikipedia.org/wiki/Trillion-dollar_coin