That's true but technical books always felt a bit tight even in landscape orientation on my Kindle.
Things like code or diagrams don't always reformat well and scrolling is a pain in the arse.
Life is just much easier with a bigger screen. Where I'd really come unstuck is when someone gives me a whitepaper or customer documentation that is only in PDF format. No reformating even if you want to.
Amazon used to sell the bigger Kindle DX but they stopped making it. So if you're buying a new device anyway there doesn't seem to be much downside to switching to Kobo, that I've found anyway.
Bigger screens are essential for scientific papers that have lots of charts and other figures. For eink-type screens there's not a lot type choose from. Fujitsu has a couple of A4 size models that look pretty good. If you can deal with traditional screens, the biggest iPad Pro is great.
Remarkable and some other companies have A5 or 10.3" screens but these are too small IMHO. You will still end up zooming and panning.
There is plenty of non-fiction that doesn't come in PDF form. It is quite readable on a Kindle.