Piracy: ꜱᴀɪʟ ᴛʜᴇ ʜɪɢʜ ꜱᴇᴀꜱ

I didn't have ads either but being able to use KoReader is a good enough motivation for me.

• You can customize it a lot to your own liking and they do something clever with page changing that it seems a lot more responsive.
• Another thing is I used to have to convert epubs to KFX to get nice hyphenation and good typography but on KoReader you seem to be able to customize all those typography things with whatever epub you throw at it.
• Also, I have a local Calibre OPDS endpoint, you can add that in KoReader and download books over wirelessly. WiFi needs to be on when doing that but with a few tweaks you have read only root partiton so Kindle shouldn't update.

Overall there are a lot of steps to it, if you're comfortable with your current setup it's not worth the hassle/time.

This is the bit I read that sold me on it.

But if you do jailbreak a Kindle, you’ll be able to install third-party apps like KOReader, which bring support for eBooks in formats that aren’t natively supported by the stock Kindle software, such as EPUB and CBZ files

I have the same doubt. I had a old first gen pw jailbroken. Recently got 10th gen basic. Not jailbroken yet

Kindle jailbreaking isn't strictly required, especially if all you want to do is sideload books. It's more about if you want homebrew, other customisation options or you just wanna get rid of ads without paying.

The airplane mode is because Amazon has a habit of updating the kindle without your permission.

I don’t turn airplane mode on and I haven’t jailbroken it. I download all my books from Anna’s archive on my phone and then send them to my kindle email address. The books appear on my kindle in seconds. No DRM issues. I have the oasis because I’m a big reader and I highly recommend it.

Not necessarily, Calibre makes this easy

They are making the OS more and more convoluted for loading your own books.

As others have said – nope. You can get a cheap enough Kindle without ads (and yes, it is absurd that there's an ad-version in the first place), and sideloading is a piece of piss. Either use Calibre or set up a Kindle email address. I mostly do the latter these days. The only downside (and the main upside to using KoReader, I would think) is that you don't get the full range of typography options sending over EPUBs this way – you would have to do a KFX conversation first (again possible with Calibre, but a bit of faff).