I would agree with you on most of the points here.
Security: If apps can share info, that should also apply to apps on apple devices. Now, I am not sure how that system works, but my methods of security are pretty much guaranteed to give results. (Using the phone only when necessary.) I'd rather do stuff on a bigger screen hence the preference of a laptop which is a different issue for a different time.
Updates: Devices today last about 3 years anyway, unless its an old school Nokia. Either the plastic breaks, or the phones start lagging, or manufacturers slow down your devices citing illogical reasons. So since you are going to be updating your device anyway, updates is out of question.
Battery Life: Mine lasts about 2-3 days so I think I am all set here. Since you say apple devices last longer, you would be one of the few people who have said so to me. It's been a running joke about how apple devices can't last a full day. I am yet to see great battery on an apple personally. I have not seen the performance of the 7, 7+, 8, 8+ and X. So, don't know how those perform.
Ecosystem: This is in fact a great point in favor of Apple, if only the devices were a little bit affordable. To fully benefit from the apple ecosystem, you'd better have the Phone, Watch and the Mac. And getting involved in the ecosystem feels like binding yourself to it. As most of the stuff is incompatible with everything non Apple.
Apple Watch: This is an area where other manufacturers definitely have a lot to work on. The current solutions are just not good. But again, if you look at the lifetime of these devices, they don't usually last more than 3-4 years. But I ended up getting one anyway.
Accessories: Apple built itself as the device for the elite and it helped in their growth. Its also the fact that, if people spend $1000 on a phone, they will easily spend $50-100 on an accessory. But if the phone is $200 you feel hesitant to spend the same amount on the same accessory. That's why accessories for high priced phones are easily available. Check out any third party accessory manufacturer, let's say Noreve (I have bought from them in the past). They offer a very wide range, but it's the premium devices that are marketed as "best sellers." Because these are the ones that sell. Just because we don't see a lot of accessories for other devices, it does not mean they don't exist. From a marketing point of view, it makes more sense to promote the product that sells.
As I have said earlier, it's more of a personal choice to go for an Apple device or not.
As I see it, there are some pluses and a whole lot of negatives. For somebody else, the positives might outweigh the negatives, and they can definitely choose to go for it. But that is not going to be me.
Security: Apps on Apple are not allowed to share information. You can cut and paste, and you can also allow the app to see some system info (such as GPS data, health data, etc.) -- though you must give those permissions. But, as a good example, I use a password manager and on Android it can Autofill my username and password into apps; on Apple I have to manually cut and paste it because of the "walled garden" Apple forces apps to run in. It is less convenient but it is more secure.
Updates: And the fact we are both here tends to show we are not "average" users. Many people are no using phones three years are longer -- looking at one site, it shows at least 20% of users are using an iPhone 6 or older. Particularly as carriers have gotten rid of "free" upgrades, people are less willing to buy new phones -- particularly as new phones aren't really adding a lot of new "must have" features. This is doubly true with people who don't like gestures, so don't want to upgrade to the iPhone X (or the ones that will release this fall) or to Android P.
Battery Live I will have to admit, on the "normal" sized 6/7/8 the battery life is not outstanding -- the have a small battery and power users will not get a full day from the battery. OTOH, the Plus sized iPhones have been quite good. In my case, with the iPhone X it works quite well -- particularly over periods where I don't use it heavily (Apple standby time is incredible). But, to give an example, my iPhone X is currently at 73% charge after 27 hr and 10 minutes in Standby with 3 hr and 30 minutes of usage. So it has lasted more than a day already, and it will be another day before I even think of charging it. By contrast, my Galaxy S9+, with similar usage, is needing to be charged daily (was charged yesterday and I put it on the charger with 53% battery today.
Accessories Sorry, I can't completely agree with your theory that it is just because it is an expensive phone. One example, why were few accessories made for the Essential phone -- it was a flagship priced at $800 at release; and is definitely a premium phone with it's Titanium and Ceramic construction -- yet almost no accessories are available for it. The Pixel is another great example; Google's flagship and priced accordingly, yet almost no accessories. But even to use the Galaxy S9+, as an example, I still can find a lot more (likely over twice as many) accessories for my iPhone X as for my Galaxy S9+; and I am looking. To give one example, Burkley cases has three pages of accessories for the iPhone X, it has two pages for all their Samsung (all phones, not just one device) accessories. Looking at Ringke (just at random, hadn't looked previously) they have 16 items listed for the iPhone X, ten for the Galaxy S9+. And this is consistent with my experience -- the mainstream case makers, while they will offer cases for most popular phones, still offer more for Apple devices. And their are smaller companies that tend to offer far more Apple, or even only Apple, accessories, than they will the Android manufacturers combined.
I fully agree it is personal choice and I don't see there being a "right" or "wrong" answer, it all depends on what the person is wanting from their phone. I absolutely love things about both but my daily driver, at least for now, remains an iPhone. Though, at some point (perhaps when there is a worthy Android watch) I may switch to an Android phone, such as the Pixel.