In my experience being able to stay on the line of attack and do irimi is neither a question of sen no sen. Nor is it a sacrifice. It is just a question of technical skills or possibilities. And a question of how you understand aikido in a wider sense.
Cutting through the attacker instead of letting him by are just different "images" of aikido, I think.
This is a video of the swordwork we do.
You may notice that shidachi doesn't move off line. But he cut's through the sword of uchidachi anyway.
This can be seen as a kind of paradigm of the tai jutsu we practice.
Completely different setting but identical scheme when entering yokomen uchi.
Irimi on the line of attack.
shomen uchi ikkyo omote.
Please notice that tori here also doesn't leave the line.