The initial mechanics were selected because they are very simple to implement, so the new functionality could be included in the upcoming hardfork. And 5% was chosen to be conservative: it should be sufficient to prevent any big swings in the HBD peg but decreases the chance for any gaming of the system.
After we've had a chance to observe how the new mechanism works, we can consider if further changes are necessary, including more complicated implementations.
Sure it's the easiest for the short/mid-term.
5% is IMO top end for a stable coin. Otherwise, the coin can become out of competition compared to other ones.
We need large Volume, the only way I see to abuse is a pre haircut massswap with higher swings, but there is a big random component also there. There is trading less risky.
So if we don't have a problem with a large amount of HBD, we should make it cheap to create them.
Maybe I will hold some too, because 3% also nice for a stablecoin.