Nova Launcher doesn't replace Samsung's extra layer of "features" baked into the OS, its skinned (often heavily modified) system apps that rarely get updates, or it's giant cache of Jellybean-era UI apps that you can't get rid of. If Samsung really wants to give people options, they should allow all of those things to be removed or completely disabled. iPhones are certainly more locked down than a Samsung, but at least the apps are all unified. Samsung devices are a weird conflicting hybrid of Android and Samsung.
It's Google's fault for allowing them to do this in the first place.
You obviously haven't used anything of Samsungs newer phones from the S8, Note 7, Note 8, or S9. Samsung isn't like what it use to be and it works very smoothly and fast. Apps more unified ?! It takes opening every app separately on the iPhone to get it to do anything where the Android will go into those apps for you. Even the Password manager will fill in the blanks in all the apps and webpages where on the iPhone it can't. Android blows the socks off iOS with usable features. iOS / iPhones are a TOY, where Android devices are a tool. And this is coming from someone who has owned every iPhone to date, and a Note 8 and S9+.