You're missing the point on how OP the wall would be if the enemy is Grounded in an un-escapable wall.
Imagine if it's Yorick vs Riven at top lane. Yorick players will tend to ready their ghouls by marking at least 3 or 4 graves before engaging, but of course, enemies with free triple hops like Riven tends to be a tough target to throw your E on. So you lock her down with W, and Riven typically became as slow & helpless as unmounted Kled. There, you can basically throw the perfect ghostly AIDS which rivals even Malzahar's kit. Also don't forget that enemies within the wall is fully vulnerable to your teammates as well.
This is the one part why everyone regards Yorick's wall being able to Ground people is simply toxic. Sure you can say his one basic counterplay is "shoot/hit the wall", but this is highly disadvantageous to top laners who don't utilize Attack Speed in their kit like Riven, Sion, Garen, Maokai & Ekko.
So like I said, if you really want to promote your Grounded idea of yours, it's best to half the duration of his W. As long as you can land your E with basically no counterplay after walling your opponents up, your new W will always be broken.