AIUI, Kobo devices have a more advanced rendering engine if you name the file with .kepub.epub. (I think it's based on ePub 3?) Not sure if it would fix the problem here. But I personally run ePubs through kepubify (https://pgaskin.net/kepubify/try/) before transferring them to my Kobo.
The graphics would be called chibis, IMO (or デフォルメ if you wanna be fancy) and IDK about developers, but perhaps weaboos/weebs would be the general term
At least they appear to be partnering with Kobo "later this year" [1]. I've been a big fan of Kobo's devices so this is a nice plus. (I just wish they could figure out some way to get Kindle exclusives, but well that's a contradiction in terms, so...)
To get a really precise answer you'd have to profile or benchmark. I'd say it's also hard to do an apples to apples comparison (if you only replace the data format in the wire protocol, the database probably still has to transpose the data to ingest it). And it's hard to do a benchmark in the first place since probably your database's wire protocol is not really exposed for you to do a benchmark.
While we're not using Arrow on the wire here, the ADBC driver uses Postgres's binary format (which is still row oriented) + COPY and can get significant speedups compared to other Postgres drivers.
The other thing might be to consider whether you can just dump to Parquet files or something like that and bypass the database entirely (maybe using Iceberg as well).
Arrow has several other related projects in this space:
Arrow Flight SQL defines defines a full protocol designed to support JDBC/ODBC-like APIs but using columnar, Arrow data transfer for performance (why take your data and transpose it twice?)
(There's also an ODBC driver, but at the moment it's GPL - the developers are working on upstreaming it and rewriting the GPL bits. And yes, this means that you're still transposing your data, but it turns out that transferring your data in columnar format can still be faster - see https://www.vldb.org/pvldb/vol10/p1022-muehleisen.pdf)
There's also ADBC; where Flight SQL is a generic protocol (akin to TDS or how many projects implement the PostgreSQL wire protocol), ADBC is a generic API (akin to JDBC/ODBC in that it abstracts the protocol layer/database, but it again uses Arrow data): https://arrow.apache.org/blog/2023/01/05/introducing-arrow-a...