Assistant just make the things at another level for me. It gives you many more options and I don't see a problem at all. even don't understand why you have problem with this topic so much.
Don't take this personally, I hope you understand that not everyone is going to agree to your views, especially one made on a whim without much understanding of the game. Look at it as an opportunity to elaborate and expand your suggestion further.
That said, I am just pointing out the redundancy of your suggestion, as most "benefits" you listed out are replicable as it is. So far the only "plus point" you brought up was the ability to set lineups, which, like I mentioned, is a two way sword. In overall, I don't see it moving any needles or improving this game in any way other than in the very rare chance something bad happens to the NT coach. It's not worth the resources spent to implement a feature which doesn't have much impact. This is one thing you have to keep in mind when pushing for a suggestion - for this suggestion to work, you might need an extra page for NT settings, they also need to program it so that NT coaches can grant other users NT coach permissions on demand. All that for saving a rare chance that the NT coach forgets to set the lineup or being admitted into the hospital? In case you're afraid of NT coaches going inactive, iirc there's already a feature which replaces them when their team goes bot.
To add on to convincing people why this feature is important, you might also want to discuss about what else the assistant can do. Will they be able to call up players? Will they have full access to NT coach features, or less? If they have the same powers, what differentiates them from the main NT coach then?
Again, I hope you don't take this negative, but rather take this as a chance to look at your suggestion in depth and improve it into something useful.