I don't think the loan and tax rates are particularly preferential.
Thanks to his twitter deal, he's had to publicize some info about how he gets his money. The interest rates on his loans range from SOFR+3% to SOFR+10%. Those rates aren't that low— even as a non-millionaire I could get similar ones from my bank (https://www.schwab.com/pledged-asset-line).
I pay 2.75% interest on my mortgage. So even Elon's best loan has an interest rate well above my mortgage. By the end of the year, his interest rate is on track to be around 3x higher than my mortgage! And like my mortgage, his loan has a large upfront payment and a minimum amount that must be repaid every year, it's not free money forever.
My effective federal tax rate is 20%. That's lower than the rate that a typical billionaire would pay on capital gains (23.8%).
That seems kinda whack to me. If I get a $500k mortgage, it's not like I received $500k of income that year-- the house belongs to the bank, and I'll be making payments for 30 years. If I stop paying my mortgage, I'll lose "my" house and have nothing to show for it except an insane tax bill (just like Elon would have to give up some of his Tesla stock if he gets margin called)
The collateralized loans trick was really only semi-viable because of historically low interest rates. SOFR will climb up to the more standard rate of 5-15% APR, which we saw with LIBOR back in the day. At that point, the one-off 23.8% capital gains tax on selling stock becomes more competitive.