Over the normal life cycle of a well designed engine (that is properly cared for), no additive is necessary. Most people don't keep a car long enough. That's why the rhetorical stance is always worded like that. "Normally speaking" covers a broad scope.
Stuff doesn't always work out that way and some service profiles can't be adequately handled by any sensible maintenance convention without issues. Some people, who are not in the majority, do keep a car beyond the normal ownership cycle.
I don't think that any additive will make your engine a "super engine". I don't think any additive will produce avoided costs that will pay for itself in terms of wear over formulated motor oils. That is, your engine is not going to wear out and the difference in utility won't pay for the additives prolonged/protracted use. Now a racer, with some unholy refresh rate, might see some longer service life out of an engine, but there the economics are a bit different.
There are some additives that can restore utility where it has been reduced due to neglect or unusual conditions.
Most of the additives that are of marginal (or no) benefit are those who allege to repair damage.
Additives that have some value, but are concessions, are stop leaks and whatnot where the repair trumps the value of the vehicle in advancing multiple costly complications. They still have value to the person who views a vehicle as a mule and nothing more. Nothing wrong with that.