[Wowfunhappy]

In the first sentence of the article you linked:

> You can downgrade (If you don’t have Shsh blobs saved) only until Apple is still signing the old software.

Saving SHSH blobs needs to be done in advance, while the iOS version you want to install is still being signed by Apple. With blobs, you used to be able to use a replay attack to force a restore. This doesn't work anymore due to the addition of NONCE, except in very limited and not particularly useful circumstances (you can move to an unsigned iOS version IF you're already Jailbroken AND if SEP is compatible).

If you know a way around this system, please do share. The Jailbreak community will love you for it. :)

Apple does everything in their power to make downgrading iOS impossible outside of a narrow window. I suspect this is also why we haven't seen any actual, definitive speed tests between different iOS versions. The discussion always devolves into "this feels slower" or "I remember my phone used to be like this," because no one can actually install an older version to test with.

[chipotle_coyote]

I'm fairly sure I have seen speed tests between iOS 11 and 12 with actual numbers involved. Someone who has a single phone and upgrades it can't do it, no, but someone who runs, say, a testing lab, or iFixit, or any other place where it's possible to have two different iPhones of the same model running two different versions of iOS can do it pretty easily. Googling "ios 11 vs ios 12 speed" shows a plethora of links from people doing exactly that. I found the same for "ios 11 vs ios 10 speed"; I didn't keep repeating the experiment past that. :)

As to your original point, though -- yes. I'd certainly prefer it if Apple didn't make downgrading so difficult, even if it's just on general principle. I've rarely been tempted to downgrade, but iOS 11 could be pretty clunky on my iPhone 6 compared to its predecessor. (I think 11.4 finally smoothed all that out, but that came out literally a week before iOS 12 was announced!)