Yeah I'm curious about this too. Been meaning to ask on the Timescale forums. My only guess is that there's some small extra overhead due to hypertable chunking.
I know Timescale has a blog post from 2017 claiming a 20x higher insert rate but that's for inserting into a table with an index. The general wisdom for loading huge amounts of data seems to be that you should insert into a table with no indexes then build them later though. So with no index, inserting into a hypertable seems a bit slower.
Timescale hypertables automatically have an index on the timestamp. To make this more comparable you could create the same index on the normal table and test the ingestion rate.
I know Timescale has a blog post from 2017 claiming a 20x higher insert rate but that's for inserting into a table with an index. The general wisdom for loading huge amounts of data seems to be that you should insert into a table with no indexes then build them later though. So with no index, inserting into a hypertable seems a bit slower.
Timescale blog post: https://medium.com/timescale/timescaledb-vs-6a696248104e