Good to see where opinions differ

Can not tell about z play but moto z is completely instant and near lag free for me on stock rom and lineage. Can not quite imagine how it could be noticably faster but as you actually can compare, i trust your judgement.
Maybe the z play feels faster because it has less pixels to render?

bt headphones user here, so 3,5mm is not an issue for me.
Battery is 1/3 bigger on play but even the Moto z has had >30% left for me when i went to sleep.

It comes down to the screen and build quality as you said.
I guess with added mod, any mm less will also be nice.
But i did not actually look out to have a moto z.
A play would have done it but then there was that 249€ offer i could not resist and now i have to convince myself that it was a good decision