People shouldn't have to have a "strong argument" to suggest a feature. We all pay for Invision products, so we're all entitled to our own opinions. If you don't think that a navigation system needs to be added—great. Obviously, a lot of others (myself included) do, so there's no reason you should discredit them for that opinion.
I think that a navigation management system is crucial, for all of the reasons pointed out above. I've spent hours trying to add links and have them display as active on the pages they are active on. It's not simple. Though YOU may not use a nav management system, I certainly will, and I'm sure others will also.
What Kyle said ^^