Based on my reading of the GeoParquet spec, the main difference is that geometries are stored as WKB using Parquet's byte array type. Byte arrays can be delta-encoded. There is also some additional metadata stored like CRS and a bounding box.

When using EPSG:4326 lat/lons, I don't think GeoParquet would give you any benefits over just having separate columns (this is what I typically do, and it's plenty fast).

If you are using range requests to fetch only parts of parquet files at a time, you could potentially sort your data using a hilbert curve, which could limit the number of row groups that need to be fetched to execute a query.