A query optimizer might do a lot better with a native integer type than a user-defined one cobbled out of int32's. It knows all the mathematical properties of the type and add things in any order, knows that x < y implies x + 1 <= y, etc.
probably easier to have this convo in email (check my profile). HN iisn't quite setup for back and forth. I'm more than willing to see your point about about a 53-bit int. I think dev experience can be made more difficult as long as a you get compensation in other areas. Email me a "hi" and I'll respond, but it might have to wait until later in the day.
If you want a good timestamp you probably want a timespec, and that won't fit in 64 bits anyway.
I don't see why it's easy to make 128+ bit types be composite, but you can't have 64 bit types be composite.
Your database driver can take care of how the bits are packed on the wire. It really shouldn't be a big concern.