Well, that's certainly true if the practice is to work on a specific technique for a specific attack without any consideration for the generality of the attack or technique - say, only teaching iriminage as a response to a shomenuchi attack. However, I think it's perfectly valid to study, say, iriminage, from various attacks (including a chest shove, I suppose). We all need to work on waza to get at the underlying concepts of aikido. With the practice of many different techniques from a variety of attacks we gain, hopefully, a deeper understanding of timing, distance, connection, posture, etc. etc.
I just really believe in letting Aikido breath. Don't try to force techniques in places. Just study Aikido.
I've seen people do it, I've done it, everyone does it from time to time. They have a technique they want to try out or do from a specific attack, and they force it. I think at that point out Aikido is awkward and we're taking a step back in Aikido.
It's sort of like trying to force square pegs in round holes.
That's why I'm animate about training in the principles first and foremost.