Yes. It is too horizontal. The reason for this is that tori is not in a position to cut downwards. Tori is not in that position because he has moved through too deeply and stuck his bum out so that when he turns, he is disconnected from uke and uke has regained her balance.
When tori is so far away from uke that he is completely disconnected and he must completely extend his arms just to maintain his grip, how big should that slide forward be? I bet I can take a bigger step back than he can take forward under those circumstances.
There are many reasons for doing it in this manner. Other things are in play. From the origin of the technique, there is a sword cut to the waist, hence sticking the butt out so in front of your partner preventing the tip of the sword from getting stuck and having the tip doing most of the damage.. This position is also more favorable to break the shoulder or elbow.
Also, if you slide forward in a particular fashion, you can go deeper than your partner can step back.