How do readers get log entries that haven't made their way into one of the parquet archive files? If the tip is some kind of live-update DB, that DB has to support concurrent readers who can't block writers. Or would you just make log messages invisible to readers until they made their way into a stable Parquet file?
Forget about DB terminology and look at what's happening ON THE DISK. ON THE DISK, is what DuckDB doing any less efficient than what your custom Parquet thing would be doing?