There are updates that I would like to have and feel they would have tangible benefits. With every android update they streamline the OS and make it faster, more efficient, etc. Google themselves tout is as booting up 2x faster for example. The big one for me was picture in picture mode, which I've been waiting for. Just to name a few. I do appreciate that Google has made some strides into fragmentation by releasing most of their apps as standalone versions that can be updated outside of the OS, but it's not enough. 8-9 months to get an OS update is pitiful. I just read that the G6 got Oreo update this week, that phone has been out OVER a year if I'm not mistaken and it's still last gen, not 2 or 3 generations displaced, so it's not like LG is doing any older phones any favors.
Anyhoo, I understand that many users could care less about updates. But for me having new features and a new OS version is very important. I use an iPhone now for many other reasons besides this, but the utterly pitiful fragmentation and slow OS updates is certainly one of the main reasons. Sure the iPhone has seen a decline in software stability without a doubt, but I don't think it's accurate to say that users divert their time to troubleshoot updates. Overall the iPhone still "just works", although with hiccups and issues that remind me of Samsung phones 3 or 4 years ago. I still think that iOS11 has MANY more features that are worth the trouble, and at least Apple acknowledges that they didn't do a great job and are delaying iOS12 to work on it.
I think "faster" doesnt make as much a difference (for many people) anymore since a few years back. I still have my note 4 (os v5.x) and it doesnt differ much in speed when using most apps compared to my s8+ wih oreo. I don't know about other manufacturers but Galaxy already have pip (aka floating window) since way back.
Like you said, android app updates have been decoupled from the OS. This is very (if not the most) important factor. My Note 4 can run latest version of most apps without issue. And that's more important to users than some academic discussions about merit of timely OS updates. However it is mostly the opposite for iphone users. You dont update iOS, then your phone is
really outdated and sometimes not fit for work. All your core apps are outdated and you can't even update/install 3rd party apps in app store (once those 3rd party dev updated their apps to latest os version)
Another point is unlike iOS where you have one-size-fit-all firmware, most android updates are programmed/customized to one specific hardware. THis ensures it runs without problems on the device it is intended for. Most probably this is the reason why os updates take so long. Another way to look at it is that you dont have to worry that updates break your phone...unlike every major iOS updates always cause issues for older devices.
I can't speak for devices from other manufacturers. From a Galaxy user perspective, updating my S8+ to oreo has little real benefits from usage point of view. All the new stuff in oreo, I already have them in Galaxy before update. The only difference I can tell is the slightly better battery life...that's all.
If you dont update from iOS v11 you do lose out a lot more in functionalities (including those "functionalities" brought about by bugs and incompatibilities

). Plus you will be nagged to insanity
I would think security would be an issue as well. Sure Android gets regularly updated with security updates, but there was a recent article about phone manufacturers saying a phone was updated with security when it wasn't.
https://www.theverge.com/2018/4/12/17228510/android-phone-manufacturers-missed-security-updates-lie I would assume that a new OS version would have all the prior security updates, but I'm not sure if that's how it works.
At the end of the day, apologist or not, you have to admit the rate of adoption is completely pitiful, just downright awful. There is no reason for it either, other than Google lacking the cojones to make it happen. Yeah I blame Google primarily, even though Android is open source Google still has many ways to apply pressure to oems, who in turn have the ability to pressure the carriers.
Security factor is much wider than you think. Like I said in my previous post, most of your info resides in the cloud/servers not on phone. You use an app then your info goes somewhere outside your phone. So your info is as secure as those who handle/keep your info. In this aspect security is the same whether on iphone or android as we are all using the same 3rd party services/apps. Case in point is the Facebook leak.
Second point is many 3rd party apps implement their own security system (e.g. your banking apps or major apps). Therefore it is crucial to have the latest apps. In this aspect, android is
AHEAD since apps are decoupled from o/s updates. You can update to the latest apps even if the o/s is not the latest. Contrast this on iphone. If you are still on ios 8, all your apps are most probably outdated (and cannot be updated as well). And I think this poses a more imminent security risk than some unpatched security holes in the underlying o/s which in most cases require complicated and non-trivial steps to exploit.
Third point is security is as good as the user. I think both ios and android are safe enough as long as you stay within the perimeter of the eco-system (i.e. you dont jailbreak or root or sideload cracked apps or easily trust any apps with your info)