There's no such thing as 'ecosystem', anymore, between mobile devices and computers. By the time mobile devices went on separate ways (and apple followed that route as well as all the others, and rightly so), this 'tight integration' just passed away. Who is masochist enough to uses iTunes to sync iPhones and iPads anymore ?
Contacts, bookmarks etc is not enough to consist an ecosystem. Besides, these features are integrated in competitive platforms as well.
I haven't synced my iOS devices to iTunes in forever, but with all due respect, your view of what comprises an ecosystem seems myopic.
It is not just Contacts/Calendar/Notes/Reminders/Bookmarks, although I think those in and of themselves are enough of an ecosystem to be inconvenient to switch away from. I also have Photos appear across all devices. I have an Apple Music family subscription and I rent movies on Apple TV. I may be a minority, but I use Pages on both my Macs and iPad.
Now, I am aware there are non-Apple alternatives for everything I just mentioned, but nothing else offers a similarly integrated and cohesive user experience.
That is not to say Apple has got this perfectly right, there is much to complain about. I still have iMessage deactivated because it was such a hot mess for me. Among my devices, Airdrop has a less than 50% success rate, which makes it essentially useless. But the over-all experience is still a predominantly positive one.