Opinions are opinions.
Mine is that a good game teaches you how to play it. That's also a fundamental of good game design. Every time I go through a tutorial I cringe b/c its just evident of a lack of the prior to an extent.
If you must see it as a learning process, then this is still learning. You learn what lies ahead so you can then use that knowledge to inform a later playthrough without invincibility. Observing and adapting, that's learning. It can also help you learn the controls while you're observing. Punishment isn't an essential component of the learning process.
While that maybe true, the onus is on the developer/designer to make an option like that unnecessary, or at the very least design the game or option around it.
I'm reminded by practice mode in DDR which is nearly the same thing, which I used extensively while playing it.
The subtle difference is that there isn't a reward for completing a song in practice mode, its sole purpose is teaching because the reward is some parts actually beating the song itself, points, and other unlocakables. Here its justified.
Granted the details aren't clear on whether or not the game can be "cleared" in invicible mode, but if that is the case you are rewarded for just effectively nothing and a lot of the incentive to even play the game in a non invicible mode is lost. That is an option, do I agree with it? No. That's simply my stance on the matter.
And Punishment might not be essential to learning process, Reward might not be either, but it certainly makes things more engaging and interesting, which are certainly prime aspects of Fun.